Well, maybe not a jig (i think that would imply adjustability).
I bought a cheap banjo on eBay, the Mulucky Maple Openback, just to see what 120 CAD buys these days (I talked the seller down from $180). Mostly it's pretty OK, except the neck was mounted a little off-center. I took it apart, and found that the lag holes were 2-3 mm off center.
I thought about figuring out a way to strap the neck down, slide my hand drill at the right angle, etc, etc. And then I remembered that I'm not a wood-working guy:)
20 minutes of design and a few test prints later, I had a nice little hole-drilling stabilizer thingy printed up that matched the 3 degree neck angle and the 11" pot radius. Started out drilling 5mm holes, and then worked my way up to 7/32.
Neck is back on, and, surprisingly, the thing is pretty playable, and sounds OK.
If anyone wants to try something like this out, the design is up here (it's customized to my particular hole spacing and heel height, of course):
A very neat solution, I am guessing it is more of a drill guide to place on the end of the neck, great .
'La Marseillaise' 19 min