The pot values make things tricky. Active circuits tend to use smaller value pots (25/50/100K), while passive uses higher values (250/500K). From what I can see the EQ-B2T has two 25K pots, a B500K pot and an MN500K balance pot. It appears the pickups connect to the balance pot and that then has a hot and ground connecting to the rest circuit.

Just spit-balling...

If you could find a concentric 25K pot you could merge the active's two 25K pots into a single unit, that would free up space for a concentric vol/tone 250K pot for the passive side. A 4-pole mini-toggle could use one pole to control power to the active unit (the stereo jack would turn it on whenever a lead is plugged in), another two poles switching the balance pot's connections from the active circuit to the passive vol/tone (500K would work for passive balance too) and the last pole could switch the jack's hot from the active circuit to the passive vol/tone. That *may* work.. but it would all depend on finding a 25K concentric pot.

Even if the above all worked out you'd still have the issue of a potential 'thump' going through to your amp if you ever switch from passive to active while everything is cranked.