An interesting wiring might be a variation of a Ric circuit using similar parts to what is in an Alex Lifeson with Piezo. It uses two outputs to provide either separate Mag and Piezo or both via one jack. A forum member over there (a2dconverter) added an indicator light for low battery. There are several posts he put in the linked thread, but the one linked below may be of interest. In the case of bass wiring, you could adapt it for the separate pickups.
Anyone install the Ghost MIDI package? Supposed to be really good, and then you'd really have a do it all guitar. :D
www.thegearpage.net
The two output jacks used are linked below.
www.switchcraft.com