Put it between the neck and the body...right there in the neck pocket. Run the output to one of the magnetic pickup's input, and you got a sustainer!
I haven't gotten into building a preamp, I don't know if I will. If you mix the piezo with the magnetic pickup you get an interesting sound, at least clean. Maybe I'll just keep it that way, as I only have a bridge pickup in that guitar (no neck). But one thing, if you actually use the tremolo system, which I don't, the way I mounted it will probably not work.
Graph Tech makes piezo saddles, yeah? Anybody tried those?