Since you already know where you want one pickup, maybe it'd be a good idea to make a mounting rig for the "non-precision position" pickup and slide it up and down the body to see where it'd sound good for you.
Found this on The Gear Page:
Basically, suspend the pickups over the strings and move them around to see how they work best. Since you're sure you want one pickup in the P position, mount that to the body and float the other one around on the rig. Feel free to set up the wiring for it so you can test how the V/V/T-V/B/T-3/V/T or whatever control set you work.
There is one small problem with your plan about no onboard EQ. In order to make the pickups blend as well as possible (without one pickup sucking the tone out of the other), pickups have to be matched by impedance (within the order of magnitude).
Piezo pickups have an impedance an order of magnitude above magnetics, and magnetics have an impedance an order of magnitude above any buffered pickup. (If you don't already know, a buffer is transparent, EQ-less preamp that lowers the impedance of anything fed to it).
To avoid tone suck, you have a few options:
- buffer the output of the magnetic pickups and controls, buffer the output of the pickup and controls, then join the output wires at the output jack. This shouldn't make it sound active as the interaction between the magnetic pickups and controls will remain passive.
- use a three-way switch to select magnetics-blend-piezo or a two-way to select magnetics-piezo. The blend will sound lifeless if the magnets remain unbuffered.
- use two output jacks, one for the magnetics, one for the piezo. You can then send each pickup to its own rig, or use a mini mixer to join them together (essentially the same as the first option.).