think outside the box then , and mount it ontop
Could use a bar piezo in the bridge.
As for the neck, I can't see why it wouldn't work. The Taylor T5 series has a pickup buried in the neck pocket.
see if you can find Randy Bretz's stealth pick up,was a mag pup buried in a fretboard,with a fret utilised as a pole piece,no reason a piezo could not be used similar,though i expect handling noises to be dominant,and a loss of treble,but that might be good in fact
I had the same issue, ended up putting a flat wound humbucker from Dan Sleep on my gas can. Stuck it to the top of the can with double sided tape. Only had to drill a small hole in the top for the wires; still had to cut out part of the bottom for the jack. Used an old piece of cigar box bottom to cover up the cut on the bottom of the gas can (which was cut out anyway in order to put a brace under the bridge). I'll try to upload an image.
I know what you're thinking, a humbucker destroys the idea of a traditional resonator. But that's not true. Played clean through the amp, it still sounds "authentic". I tried both a piezo disc and a rod, but the feedback with the metal can was unbearable.
In the bridge is a favourite, its what I do, among other locations. You could put one on the peg head if you wanted but I feel closer to the source of the sound is better. Mount the piezo on thin timber before gluing into the inside of the can. You can vary the tone a bit.
.........or you might use a larger than usual pickup surround to add stiffness to the pickup cutout.