Hmm, I have seen a quick-change battery setup on here before- long time ago though, so the thread is nodoubt burried.
A hinged battery holder strap/plate with a simple locking mechanism at the other end would be good for a quick change over- if you can incorporate the battery plug(s) into the strap then all you would have to do is close the hinge to connect up the plug; Im thinking bullets would be good or those ec5/ ec8 connectors from losi maybe.
Spiffy drawing can be supplied if needed
This would need the shell to be removed to do the change over though, but a sideways removal version would work too- lots of custom work envolved either way.