Steve,
I do the guitar/kb switch every now and then, and my guitar of chouce is the Parker Fly .... it's SO thin and light(less than 5 lbs) - no trouble at all reaching around it to tickle the keys.
It's also a concave shape so it "hugs" your belly instead of protruding outward like an Ovation roundback. Sweet instrument. 2 humbuckers and a piezo transducer under the saddle. The acoustic sound is amazing.