Mike,
I am sure all those sleepers are mounted to the frame. Most are set on solid rubber bumpers though. That's not as nice as air ride.
I am not sure I would want to try to extend an existing air ride integral sleeper, then move the air bags back. It could work, with real good craftsman, but I have never heard of anyone doing it.
Larry
http://onezman.tripod.com/onezmans.conversions