What kind of functionality do you want ? Just a buffer ? Or EQ ?
Years ago I cloned the active circuit (passive PUs) of some 'special'-P-bass-version. The Fender-circuit uses around 5 NPNs and a PNP and does Bass, Treble, Volume and some LPF-shaping. Sounded good as far as I remember. Runs of a single 9V. Let me know if interested.
It's probably quite alike to the Shadowsky-circuit from another thread here, but that's just a guess.
Bye,
peter