Anyone who can use a screwdriver and a soldering iron can retrofit an electric guitar with a piezo bridge (look up fishman or graph-tech for active and passive piezo bridges).
I've retrofitted several guitars with passive piezos already (less work than active piezos as you need no battery cavity ... with some EQing and a multiband compressor you can make them sound almost identical from my experience) and can only recommend doing this on your own.
If you want to avoid any drilling or potential damage to your guitar, I recommend filing a small hole on the bridge pickup mount, then put the wires of the pickup through there. Then add colored insulation for the looks and replace the output jack with a TRS jack.
Check out the post below:
http://forum.fractalaudio.com/lounge/68752-any-experiences-diy-adding-piezo-bridge-2.html#post851791
Takes only several minutes to do, looks great and does no damage to your guitar body at all.
The only thing you should take care of is checking if the bridge is compatible to yours in terms of size (so that the distance between the screws is the same). Check out the specs of the bridge pickup and compare them with measurements on your guitar before buying a piezo bridge. This should more or less be standardized for typical assembly-line guitars, but certain guitar manufacturers might use custom bridges.
The output of passive piezos is stronger than that of magnetic pickups and the piezos also generate much less noise than regular pickups, so you don't have to worry about that aswell. Getting a quality TRS to double-TS cable is a pain in the ass, though (as the Axe doesn't have a stereo input jack). But you can always make them yourself.
