Lots of people use aspen substrate. I've tried this but I can never get it all clean! I do keep a pile of it in one part of the cage for my boas though...
Also, with the type of substrate you're talking about, I would think that the snake is going to have to burrow down all the time just to get the heat; maybe I'm wrong, but if you use UTH then it makes logical sense
I use the cages at http://www.reptilebasics.com They are the bomb diggity!!! Just more info for you
I'm also digging the radiant heat panels that they sell. Heat from above that won't burn the snake and yet warms like the sun and substrate is not a problem. Very nifty little invention!
Also, remember a thermostat!!