I literally just finished work on exactly what you're talking about. I wanted my old crappy $80 acoustic to have something unique to it, so I took my old (also crappy) Precision pickups, and tried putting them in. I found a way to mount them, just screwing them in to the sound hole, but being as smart as I am, I forgot to test the string-to-string pickup before installing it that way, and my high, and low E's barely picked up. I ended up taking the magnet from one of the two parts of the pickup, and putting it on the top of the magnetic poles, increasing the surface area, and mounting it in an elaborate plastic case I found, and blah blah blah.
The end result was a week of work to mount the pickups wrong, months of pondering what to do with it, then 12 hours of cutting, soldering, and screwing to get a really bluesy, fat sounding acoustic-electric (that I forgot to ground, which I will do when I can be arsed). The lesson is to think everything out, have a solid plan before trying anything, make sure you know exactly where the bracing is before drilling, and don't do anything permanent before testing it's feasibility.
My camera is charging right now, so I'll put up pictures in an hour or two.