I noticed someone selling those (rubber?) pads that go on the ends too.
I was thinking about this last night. You'd just need to find something like a coin or button, then make a shallow hoop and secure it to a smooth surface(like wax paper.parchment paper, waxy side up). Pour in some flowable silicone, remove the excess, let it cure for 24 hours. Trim t fit, adhere with some sort of contact cement or super glue. Another option is similar, just make a rectangular mold, pour to 1mm depth(or maybe less) with flowable silicone. If you've ever bought One Drop Flow Groove pads, it would be like this except not so thick, but same idea: strip. If you can punch to proper size, that would be ideal, otherwise, perhaps a trace with a Sharpie then skillfully excise with a #11 Xacto/surgical blade. Another idea would be if there was a really thick/rubbery tape that could be cut up, but I don't know of any. I also had to use some of that Leak Stop, and I would think if that was sprayed onto a surface coated with a non-stick spray, it could be sprayed on and left to cure. It sort of levels out a bit, but it's still kinda sloppy and messy to use. Might take some practice to get the depth good but could probably be sanded to proper thickness.
