They do make thin drywall for what you are talking about. About 1/4" I think. They may even have thinner rock, I'm not sure. A lot of times I have seen good rockers score the face of the panel in as narrow increments as 1" and glue and screw the panel to the framing, but talk to some drywall outfits around you. They probably have even more ideas that could work better for you.