I'd advise measuring it just like you would a regular finger.

On mine, I typically use a quarter scale, center it on the bridge and go on a 20-degree angle down from the ring, leaving a 1/2 inch between cuts. I think pitch it away the same amount I pitched the ring. I also use 0 or reverse pitch with a lot of bevel in the hole.

In my experience, you don't want to consciously know that finger is in there. It's not something you should actively be trying to lift from (unless that's your goal).

Jess

If you do the thing where you put your thumb in the ball, lay your fingers out across the ball and the leading edge of your finger holes fall halfway between the first and second joint of your fingers, then I would advise using the same method for your pinky.

The pinky doesn't need to be quite as precise, since it's not going to be a true "lifting" finger (although I do impart a little lift with mine). Its basically going to help you with ball stability on the hand. Every time you add a finger into the ball, you divide its weight across another surface, plus you gain some lateral stability (the ball won't be as easy to shift side to side through your delivery). Where you'll see the biggest difference is in the pain (or lack thereof) in wrist tendons, and a decrease in the likelihood you'll get "golfer's elbow" (the opposite of tennis elbow and the condition that most affects us as bowlers in that joint).

Where people get messed up with pinky finger holes, I've found, is if they drill them in a way that doesn't allow their hand to trigger and clear at release. I would say it took me less than 5 hours to get accustomed to the change, perhaps I was lucky. Cutting down revs is a common complaint and I have to believe those folks either are drilling the hole too close to the thumb or too far away from the other fingers. When done properly, it mimics the effect of keeping the pinky finger tucked.

Jess