Actually I just ordered a pickguard to do something along those lines... P-Rails in Neck and Bridge. DPDT On On On to get parallel/rail/p90 selection options plus a RWRP single to pair with neck rail / bridge p90 for hum cancelling option. Plus and on/off toggle to get Bridge/neck combinations.
I considered series instead of parallel but 1) I have an abundance of 2 humbucker guitars and far too few single coil options and 2) Its a Strat... of course it needs to be a tricked out science project. I cannot possibly have 2 Strats basically identical. 50's Strat decked / hotter 70's w/EJ and Gilmour mods / Brian May wired Trisoncs / P90 science project.
I will use a 500k pot with a resistor on the middle single coil to take a little top end off depending on what I put in there. The 500k's should work well with the P90's which is the primary focus on this one