Legally both of you are responsible. However I am sure there are ways to persuade legally to get his ass in gear.
A. Tell him that his room is now on CL for rent because he can't pay rent. Shit will get real when someone comes and talks to you at the apartment. Could shake some sense into him.
B. Got any friends that would let you crash at their place for about 2 weeks? If so, turn the power off, the gas off, everything for about 2-3 weeks and stay with a friend. Again, wake up call. He's either gonna pay or freeze to death.
No other legal ideas as of now, but I'm sure I'll think of something.