Original Gibson 3-pickup LP Customs were wired as follows: up on the pickup selector, neck pickup only with volume and tone controlled by the two knobs closest to the strings; middle position, middle and bridge pickups together out of phase; and down on the pickup selector, bridge pickup only with volume and tone closest to the edge of the guitar. This obviously doesn't allow for some good-sounding combinations, like neck and middle, neck and bridge, middle and bridge in phase, or all three together. Epiphone wires their G400 (SG) Custom with the selector giving neck, bridge, or both together, with three volume controls, one for each pickup, and a master tone. The middle pickup isn't wired to the switch at all, but it can be brought in and out with its own volume control. I like this setup, as it allows for any combination of the three pickups while retaining the vintage look, without adding any extra switches or knobs. You might consider doing something like that to your LP.