Another and cheaper option would be to install a series/parallel switch on your jazz. Incase you don't know, a Jazz bass' pickups are wired in parallel (so they work as 2 separate pickups) and a Precision's are in series (the two halves of a Precision pickup are actually two single coils wired together to act as one whole pickup. This gives a P bass it's extra oomph). By having a Jazz bass' pickups wired in series, the bridge and neck pickups will then work together like a Precision's does and give you that extra oomph.
Usually achieved by having a pull/push pot on the Jazz neck pickup volume knob. It would still be your regular Jazz, just click up the vol pot for P-bass like fatness.
@Ki0gan is a basschat member that can supply such a thing very reasonably using top quality components that are easy for anyone to install.