I have done it to an old Custom 24.
If you want the cables from the saddles to be completely hidden you'll need to drill a hole on the trem base to run these through the trem and another one to take them to the pickup cavity.
Electronics all fit in there.
I removed the tone pot and replaced it with the piezo volume and left the mini toggle switch in the pickup cavity so you couldn't tell any mods but looking at the guitar.
I blended the signal using the 2 volumes.
I'll try and dig up some pics...
The white thing is the double sided tape under the piezo pcb board.
This could be glued to the backplate, but was also fine as is. The piezo volume also had a push pull mid/bass boost IIRC....