The
Seymour Duncan Pickup Booster (
schematic) has a resonance switch that puts a 1n or 3n3 (or no cap) between Q1 base and ground. This moves the resonant peak lower. Combined with the subsequent boost, it lets a single coil pickup mimic a humbucker (still hums though).
I don't know if that's what the Firebottle uses, as I'm not familiar with that pedal. But this trick works pretty well, as long as the pedal is first in the chain. If there are any active devices between the pickup and the cap to ground, it won't work.
You could just as easily add a similar switch to your guitar if you wanted to.