I need to drill a backup ball drilling- left handed drill for right handed bowler. I was wondering if there were any differences in finger, thumb pitches for backup bowlers for comfort.
I know from experience that when I try to use my regular layout, span, etc. trying to throw a backup ball hurts. The ball doesn't exit the fingers properly. Any advice to ease comfort of the bowler would be appreciated.

That's an interesting question...
Is the customer male or female? It makes a difference physiologically.
To me, the important part is making sure the lateral pitch in the thumb is correct. For example, having right pitch in the thumb for a person throwing a hook (rotating around the ball from 6 o'clock to 3 o'clock) would necessitate having either less right, or maybe even left for the same hand structure rotating clock-wise to throw a 'back-up' ball.
There. That answered nothing.

The bowler is female... I am not sure why, but come to think of it, every bowler I have witnessed is female... hmmm? I wonder why that is? I have never had to drill a backup bowlers ball before, and wanted to make it more comfortable for her. Thanks

Plamormick is correct on the thumb pitch. Their thumb comes out of the ball totally different. Also, may want to consider dropping the middle finger hole 1/16 - 1/8 due to where it normally ends up a the release point in a backup ball release. I have a sr. bowler, male, that does this & he is not bad averaging 165-170 this way. He is rt. handed but I layout the ball out, pin/cg/mb wise, for a left hander & he got better ball reaction that way. Good luck.

Thanks guys for all the help.... I drilled it up, and she loved it. Most comfortable grip she has had to date. I plugged all the holes in her ball, and set it up with left handed layout. Time will tell with her scores. She is one of the highest average women at our center already.

I knew there had to be some reason for more women with a backup ball, just didn't know why... Thanks again