Bruce,
I have not had to glue veneer on my pocket doors yet but I had thought about how one might handle that issue if I had the problem. My thought was to position the door so that some synthetic shim shingles can be wedged between the pocket surround and the lifting veneer on the door panel. Probably have to shim both sides to hold the panel rigid. On the exposed edge of the door, away from the pocket, the lifting veneer should be able to glued using clamps and wood blocks.
I have not had good luck with the Gorilla glue that foams and expands, while it may be strong, in my case it hard to keep it just where you want it. Gorilla makes a good white glue that I would use but I personally like Tightbond, some wax paper, and the use of a palette knife. I think the Tightbond seems to work into the tight spaces a bit better. I clamp once to remove the excess glue, wiping it with a dampened cloth, and then clamp it again. I use the palette knife to shear the second clamping excess when the glue is partially dry.
I have not tried Steve's heat gun idea but it sounds like it would be a help. Good luck and let us know how the repair works out.
Later Ed