Back in the late 80's I used to winter camp a lot with a college buddy "Chris" fishing Moosehead Chesuncook and Mattagammon in northern Maine. Unfortunately, it is hard to find people that want to do that sort of thing these days, present company excepted. My girls did when they were in my early teens.
Well back to the feet thing: At about mid-night one night Chris stumbled got out of the tent went out for a few minutes, then returned with the statement, "Did you ever notice that when you take a leak your feet warm up." I said no I try not to P^** on my feet. "Well I didn't, I don't, I just mean... " We laughed for at least an half an hour
So try Chriss's method it works for a minute or two.