i remember reading a thread on ultimate guitar where someone made a tutorial on converting 2-conductor pickups to 4. Maybe try searching over there in the gear building and customising forum?
bear in mind, i have no idea of the accuracy of that tutorial, and if they were sweet, old (i.e. irreplaceable) pickups, i probably wouldn't chance it myself. It seemed to involve a lot of ripping the wires apart, if I remember correctly, you could doubtless do some major damage if you weren't careful...