My boy is from a 20G community tank, though, in which everyone else is doing their thing like normal. I didn't want to treat 20G worth of water, either. I suppose it would help to include that info. xD
I found this really cool submersible heater from ZooMed. It's built for small tanks. You put it an inch under your gravel and it heats the tank up for you. It works really well! It isn't adjustable, but the temp hasn't gone below 80*F since I've been using it (keep in mind this isn't that long. Only one day).