In July, 2002, Mica wrote the following about a modification for Persuader electronics; note that the price quote is probably outdated. I believe the difference between Persuader and Elan electronics is that the Persuader is Volume, Volume, Filter and the Elan is Volume, Pan, Filter. And I believe that, like the Persuader, the Elan has only one preamp. So I'm guessing this modification would work for an Elan.
The P pickup is one of our loudest pickups, and the JZ is one of the softest. Add that to the positioning with the poor skinny JZ pickup back where the string doesn't move much, and without a separate preamp for each pickup, there will always be a volume difference between the two. Currently you have one preamp and one over gain control inside the bass.
You could send your bass in for a modification to add a preamp for the bridge pickup. This will give you a separate gain control for each pickup so you can set the height to where you like the quality of the sound, and then adjust the gain so the pickups are of equal volume. This is all internal work, and the exterior of the bass will not be affected by the modifiactions. This will run about $350 excluding shipping charges.