I'm uncut. I tried the ESL40 and it tore my frenulum, ruining it for good. I then switched to the lingam extender but I find it a bit inconvenient. I have noticed that if I grab my foreskin between my index and thumb and pull, the force gets transfered to the shaft, which gets stretched. Maybe it would not be a good idea to apply a lot of force to the foreskin but I could totally imagine building a harness that pulls ever so gently on the foreskin to keep the penis stretched throughout the day. That might still be beneficial and would only have the downside of potentially causing me to end up with a lot more foreskin. I need to find a way to comfortably clamp down the foreskin in a way that doesn't hurt or block the circulation much. Any thoughts?

I don't think one should pull the foreskin, but rather retract the foreskin and pull from the glans.  I suspect that's why you tore the frenulum.

I haven't been pulling the foreskin. I tore the frenulum because of the ridge of the ESL40 (and the lingam extender)

What's the Lindam extender?

@Peyron I think that is a great idea, using fingers you can generate a modest amount of tension and it spares pressure on the frenulum.  If you use three fingers and thumb it seems more comfortable and secure.  I would imagine the difficulty would be to find a way of clamping that the foreskin wouldn't just slip out after a short time. When using your fingers, you can sense where it's needed to adjust the pressure and regrip easily when needed.

I was thinking some "sticky gel pad" products would help with grip, which could be cut to fit a clamp. or 'liquid chalk'.  

For a clamp, something that can be strong enough, preferably adjustable tension if possible, but if it uses a screw you have to be careful it's not in a way that might risk getting the skin caught in screw threads. it might need some wider and extra grippy materials fitted to the jaws to get the right grip area. I thought of:

medical bulldog clamp: Bulldog Clamps 9cm Straight with Spring Tension Adjusting Screw
ordinary office supplies bulldog clamps - but not adjustable , maybe not strong enough?
woodwork/diy spring plastic clamps - but not adjustable
adjustable guitar capo - would need adding materials to reduce the gap between the grip surfaces.  
hair grip - probably not strong enough.

@Peyron, I was in Poundland today and bought a pack of 4 plastic spring clamps for £1. There was only one size. One of these is quite strong, and can apply a substantial stretch. I didn't even try to tie it to my extender top piece as i expected, as one of the handles could just be pushed into the socket (it's a Chinese one similar to the PMP).
It does seem quite viable for at least about 10 mins or so, but after that the skin was starting to feel a bit sore, but it seems to have some potential. The plastic clamp "teeth" are far too hard to use uncovered, but I covered them with some thin latex material.  The tension seemed about right but possibly inserting a larger clamping surface would be an improvement, and probably some cushioning.  Of course there are also bigger/stronger clamps of this type.  I also looked at some hair clips and clothes pegs as well, but thought they would not be suitable or strong enough. I could not find any large paper clips, but  imagine that also might be a possibility.

Hello,
Yes... There is a devirce that will safely grip your foreskin. It is used by men who feel agreived for being cut, or for guys who want to grow foreskin for medical reasons. (I fall into the latter category). It works by placing a small 'egg cup' shape between your foreskin and glans. A small pole is attached. A rubber cup fits over the onto of your now moulded foreskin shape to grip. An elastic can be attached to the pole. In turn attached to your knee. Causing a stretch. I bought the device about a year ago. You will get traction but you will DEFINITELY GROW your foreskin. Upto double in size in a year. Having owned an andropeyronie traction device and the aforementioned. I can tell you the andropeyronie device definitely gives stronger traction. Although the aforementioned will also give a pleasant traction. Can be worn for hours and is painless. If your interested? I'll try and dig out the name and contact of the supplier.

I think this sounds iffy at best. Traction therapy won't really work unless tension is provided to the scar itself.
You don't even want to apply hard traction to healthy tissue, which can cause venous leaks.

In any case, i recommend watching this video: https://www.youtube.com/watch?v=82g7ViTj94U&t=2260s
It describes how to loosen the skin at the base of the device before applying traction. In general the skin on top of the penis should be loose and no or very little traction should be applied to it.

@MrMen, I was aware of foreskin restoration devices, not seen one in person but had seen a photo of a device similar to that description, except for a not having a knee attachment. It was designed to apply tension to the foreskin, but not to the penis body: it does use an elastic band for the tension, which is attached to a pole which directs the force down against a cap on the penis, compressing it,  the opposite of what we want.. although your device you've seen must have used a knee strap to apply tension, am sure it would still be designed to apply tension to the foreskin specifically , not the penis body.  i.e. it would have to be be attached to the gripper, not the pole.

MrMan, of course that would be helpful for growing the foreskin in the first place, and the more foreskin the better I guess for this.

I've seen a site with a device like MrMan describes, and it can apply a tension to the shaft as well as foreskin , by using suction.. It does have models with a pole but that's  for the foreskin restoration function, so if we have enough foreskin we wouldn't select that.  
Jelqtogain looks to have a very similar design, he does say it's meant more for keeping the penis elongated during recovery, rather than a stretching exercise.. both sites have videos of fitting it

tlctugger.com/product/vlc-packer-stacker-kit (or the other ones without the pole would be suitable)
jelqtogain.com/store

there's also an aliexpress similar style foreskin restorer without a tugging attachment, that is what I had seen before. (cheaper but looks it)