The problem with adding a weight hole is that the CG is basically in the center of grip for the vast majority of full-roller balls. If not in the center it's darn close. Thus there's minimal side, finger, thumb, top, or bottom weight. Adding a weight hole anywhere will add weight on the opposite side of the ball and possibly make the ball non-compliant if the hole is large enough.
Better to use surface changes if he's looking to handle more oil. Or, even better, get a stronger ball made to handle more oil. Due to newballitis, his scores are sure to go up.
SH