The electric blankets and heating pads are crawling back out of the closet as the cold weather sets upon us. I have seen several front page posts of cats laying on heating pads. But our 4 legged friend's skin is much more sensitive than most people think. Because most animals don't sweat, their skin doesn't dissipate heat as well as ours.
I personally let my cat lay down on a heating pad set to low for 10 minutes before she got off of it on her own initiative. She had burned her whole left side and was freaking out licking herself and spinning in circles. Asked 2 different Veterinarian friends of mine and they both mentioned that even with surgical warming pads common in a lot of practices, even being designed with animals in mind, burns are all too common and their use is usually restricted.
I know it seems like a nice treat for your pal but the risk is too great. Please don't let it happen to you!