You need a thermostat. Here is a thread I posted (graphic) of someone who "thought" a UTH without a thermostat would be just fine. Your method of "using more aspen" won't work, especially if he burrows. Don't risk it. Don't be cheap.
btw, im not tht kid from the post in west virginia, and there are plenty of herp vets around!
Reptiles
0.0.1 - Rhacodactylus Ciliatus, Cheerio
Mammals
1.1 - Canis Lupus Familiaris, Little Man & Molly