Hey Subby. Welcome!!!
I am pretty sure the ES2 pup has three piezo sensors embedded in the bridge, just behind and touching the Saddle. No sensor under the bridge.
I believe you would need to replace the bridge, or drill it to install the sensors, and the preamp would be another ball of wax... or ball of confusion.
I suggest a K&K under the bridgeplate, if you can get in there. Much more simple and sounds excellent too!
Good luck on this interesting project.
Stay vigilant and stay well
Paul