When my uth got too hot for my liking, I simply placed a thick terrycloth in between the uth and the underside of the viv. My viv is a plastic faunarium and the uth was never stuck to anything...I didn't remove the plastic sheet on the sticky side. That way, you can move the uth from viv to viv if needed. If it is still too hot, I just double fold the terrycloth and it dissipates the heat quite effectively.
Years ago, when I kept White's tree frogs, I had stuck the uth to the aquarium and I ended up having to place ceramic tiles inside the tank to help dissipate heat and to prevent the frogs from burning their bellies. You could always add an additional layer of tile inside your snake's viv if it is still too hot. And they are also very easy to clean.