OK, I was having this problem just recently. You have a couple of options that I can think of right now:
1. Space Heater- get one thats really safe
or
2. Another UTH or heat device- but then you gotta buy another T-stat, unless you have one that can control multiple output temps.
or
3. put your snake(s) in a room that doesnt get too cold- My Dad's house is always around 70, so I insulated one of the closets to convert it into a snake room.

hope that helps