Molding your hand in that manner is likely the only way to get the grip custom fitted exactly as you wish.
You will have to hold it exactly right and keep it from running until the JB sets, maybe three hours or so? Or you could use a roll of plumbers epoxy putty, it usually sets in maybe 15 minutes. It is plenty hard and strong enough to drill and tap so I think it would be durable IF you properly prepare the stock.
I would sand the stock grip area I expected to apply the plumbers epoxy to, then drill a series of small holes, about 1/16 and 1/8 deep, all around the area before applying the putty. That would give both a good surface and some good anchoring points for the expoxy to adhere to.
I get that epoxy from Home Depot and Lowe's, in the plumbing departments. It is in a plastic blister tube and about the shape and size of a Tootsie Roll candy bar. It's usually gray but they also had green. It's much like kids modeling clay, very easy to mix with your fingers, reasonably quick to set and easy to mold while it's soft.
Wet your rubber glove with liquid hand soap for a release agent and it will leave a slick surface to ease your sanding later.
