I've seen a glider towed up once. The most important thing I saw was the speed. Too fast and the glider does snap rolls. It was cool. So, to sum up, make sure that your plane has power, not speed.(large, low pitch prop) As long as your plane can stay up for 10 minutes that should be plenty of time for towing gliders.

Back to the fuel issue.
What I would do if you really think it is necessary, put another tank in the fuse, put the engine exhaust to the exhaust attachment on the second tank. Then take the second tanks clunk and move that to the first tanks exhaust deal. Then take the first clunk and put that to the engine.
I don't think I would bother though, unless you want endurance.