Vintage Vibe Guitars does a side by side, split coil in a J form factor. It is a J pick that sounds more P then J. Has the advantage of being humbucking and quiet while still retaining the single coil punch, clarity and articulation. Still has a bunch of J in it though as physically, the J pick is just plain different. I commissioned the first set from Pete and was happy with the results. You have to email him on that as it doesn't appear on his website as a separate pickup. Info@vintagevibeguitars.com
Your other option is going the Reggie Hamilton route. By which I mean, mr happy router comer out to play and you drop the split P of your choice through the hole in that custom pickguard you also ordered, into the hole created by mr router.
If ya really like the rest of the bass a ton, get a luthier to do the rout... Otherwise buy a routing template for the split P and whirrrrr away!
I like the PJ combination a lot. Have an 83 Fullerton P that began life as a standard, the got a BA II bridge and the happy router treatment, though that was for a J at the bridge. Then it got a MIA J neck. It is my goto, utility, take it anywhere bass. Though I get romanced by other basses in the stable, that one just sticks...
If you really want that solid as a P Bass thing going on... It's happy router time!
Pete makes a bitchin' split P as well. I like mine in Alnico III magnets with 2 coil taps. 1 at 'standard' and 1 @ 5 - 10% overwound. Wire it up with a push pull pot... You go clean to woofy in a pull
Either way, your wiring is going to change... Easy, peasy...