Go get a six quart (or similar size) latch box. They're $2-3 at WalMart or Target. Poke some ventilation holes in the sides or lid.
Remove the cage décor from your tank and push the aspen over to the cool side.
Put the latch box into the tank so that 1/3 of it is over the heat pad. You'll have to adjust the thermostat controlling the heat pad so that the surface temp in the tub is 86-87*F.
Put some aspen into the latch box along with a small hide and water dish.
Put your snake into the box and secure the lid.
For privacy you can cover the latch box with a small hand towel or piece of newspaper.
Colubrids like king snakes, garters, corns, milks, etc. do ok in cages, ball pythons just don't.