Just thought of this yesterday, too, and kind of surprised there aren't any examples of it done. My thought would be a single coil guitar (strat?) replacement pickup (essentially a Musicmaster or Bronco pickup). Unfortunately there are 100's of options and no track record of them being used at bass bridge pickups.
The biggest problem I see (once you have pickup in hand), assuming you're using a spacing similar to a Jazz or P special, you'd have to notch the bridge plate to fit the pickup. Doing it tele style with the pickup in the bridge plate would be too far and butting up against it even would be too close to the other, I think? With the MM/Bronco bridge, you'd be clear though.