Yes, I've got a Graphtec piezo bridge (though it's individual leads from individual saddles as it's a Tele), and so far have have routed out channels under the bridge plate for them to run through holes I drilled in the bridgeplate and into the bridge pickup cavity. There they run to a 6-into-1 circuit board with a single output lead running from it off to the graphtec piezo control board. My control board seems bigger than the one they've used and I haven't got the space to fit it in any existing control cavities. The standard Tele control cavity is only big enough for its own pots and switch, while the pickup cavities are full of pickups. So I need to rout out either one big cavity to fit the battery and control board in or one for a battery box (back of body) and another for the control board (probably under the pickguard). I'm getting more confident with my routing, but I'm still rather apprehensive about doing it wrong.
The piezo control board does have an input for magnetic pickups, but I was trying to keep the magnetic and piezo outputs separate (it's designed to use a blend knob but I'd need extra pots on the guitar) and using a 4-way switch so that one position selected piezo alone and the other 3 the standard Tele positions. I'm not 100% sure how the pre-amped piezo output will work running through standard volume and tone controls though. I'll re-read the instructions again and see if I could use a switched pot and run everything through the pre-amp and still select mag or piezo only.