I'd suggest using something like a 2P6T rotary, that is, something with two common poles and six rotational positions (left half of the image):
Use the left common as input and connect the left 1-6 to different electronics or preamps. Then connect the electronics' and preamps' outputs to the right 1-6, and the right common to the output jack. That way you'd be able to rapidly switch between tone stacks and test which one's best.
Maybe you could build it into a small box, connect it using an extremely short (10 cm) cable to a bass with no electronics in it whatsoever (except maybe a blend or pickup selector switch) and attach the box to your strap. The cable'd be short enough not to impact your tone (as longer cables might).