I know I saw this cheaper just yesterday, but I can't seem to find it now. I was looking to do the same thing with my Spirit 2M

http://www3.towerhobbies.com/cgi-bin...?&I=LXZ904&P=0

I think you could design a receiver for the gearbox/motor so that it's easily removable to install on your other glider. Maybe a plywood rail?

It looks like a good unit. You could use a small, like 700mA two cell LiPo and a ESC. You would probably have to keep your RX battery though or get a ESC with a programmable BEC and set it's cutoff HIGH so you have enough RX battery to fly for an hour. In that case I'd go with a 1500mA 2C LiPo. Just thinking it out here for my benefit too. You really only need about 5min of run time to gain altitude, so I think the small LiPo with your RX battery for the radio gear would work and keep cost down. I'll bet it won't weigh any more than the little glow motor, tank, fuel and throttle servo (if you run a servo)