Its doable (one of the guys from judas preist does it and jason krauss from kid rock does it as well, Maybe even rustey cooley not sure though). Most of those circuits are
les paul style wiring (if you can call it that), with a three way toggle, two
volume pots and two tone controls. That would be the easiest to do in my opinion but who knows. This is something I wouldnt mind doing. You may be able to have emg wire you a new circuit and leave it open for the passive pickup. WHo knows. They do sell premade harnesses though. Id suggest getting an 81 and 85 and saying to hell with it though.