I think I understand now. You're wanting to be able to separate the cast off of the denar mount side. First before mounting paint with sodium silicate for separating. Do your business, then just use 50/50 Elmer's glue and water.
You want something faster then hold the cast to the pattie.. put a bead of super glue around the edge. Then rub it in with a q-tip. That will be strong enough to hold it together around the perimeter.
Now if you don't care what it looks or you're not wanting to send it back on the mount, skip the glues and get a hot glue gun.
There's several ways to do it, however if you key your cast, you can skip any fancy, accumulatively expensive gadgets to use in mounting. Just go back to basics.