Robart makes a very neat drill jig tool for hinge points. It comes with two different size bushings and you can order another directly from them. It's made to work on either constant thickness surfaces, or tapered.

http://www.robart.com/New%20Pages/Hinge.html

Scroll down to the middle of the page. It's item #319 and I paid $4.99 for it at one of my LHS's.

John