I'm trying to drill a ball for a guy who bowls in my league.  He doesn't use his thumb, and as hopefully you can see from the picture, he goes across his middle finger.  I tried to highlight the track with yellow grease pencil.  The white tape below his thumb hole is where I estimated his PAP to be.  I had him throw the ball with tape and, it was pretty close.

I am not trying to fix his release, which is probably the best answer.  But I think this is a over rotated full roller?  I would think you would want this ball to flare as quickly as possible, but then again, that might just make him flare over the ring finger.

Any suggestions on ways to drill a ball for someone like this?

I have a bowler like this that I have drilled for. His PAP was 2 1/2" X 1 3/4" down. A lot of his stuff would be pin under or drilling out the pin as that would equate to a 4" pin to pap. My advice would be to trust your eyes. As odd as this may be, it's no different than any other bowler. Get his stats drill the ball accordingly and apply weight hole and surface as needed.

With that said. His stats are going to be essential, moreso than most. If he is a high rev low speed bowler like what I deal with then smooth surface and strong weight holes will be key to getting the ball to transition smoother downlane.