Just out of curiosity, what are you trying to do? Is this for a gig or a recording? I've never really understood the giant on-going discussion about P's and J's on here. They are different, but they're also very much the same-kind of a standard passive bass sound, which you can do a lot with of course. In a band setting, unless it was something really specific I can't imagine many people caring too much.
I can understand it from a "being a bass player" perspective. I've often wished on a gig that I could easily switch from a Pbass with flats for one song, a jazz bass for another, and an active 5-string for a third, but any will really get the job done for most tunes (caveat, I don't even dabble in metal or many other far from pop/rock sounding stuff). All of that to say, if you're too broke to buy another and not wanting to drop a jazz pickup or some active electronics in there, what's the hurry? What are you hearing out there that you wish you had?