Thanks to everyone for your suggestions.

I lucked out over the holiday. While talking to a cousin, he pointed me to where I could find what I was looking for.
(of all places...... Cabela's. Imagine that! )

The stuff is called Form-a-Grip.
Starts off as a putty and cures into a hard rubber. It is usually used to make overlays on grips that conform to the hand and fingers but you can build up low spots also.

I'll be ordering a can of it this coming week. I'll post how well it works when I am done.