Is it just the tailbiting thing? Other than the heater issue, why can't you keep him? Others have also offered to chip in a heater if that helps.
If you need someone to take him, I can (5 gallon with heater. My previous betta died from a bacterial illness so I'm keeping my eye out for filling up the space again), but you'd have to ship pretty far, and I know you'd prefer not to do that. Hope you can find a solution
♥♥♥ My betta fish, Melanie, was fortunately adopted by me from someone who had received her as a Christmas gift and didn't want her. Please do NOT give living beings randomly as gifts. R.I.P Summer 2013
♥♥♥VEGAN LIFESTYLE <3