GGJames,
The solution is in FM9-Edit in FC Edit. There are two "parts" of a footswitch, a toggle, and a hold. Both do as they sound, one "toggles" or "taps" to perform a specific function, and hold (press and hold) for a determined time performs a separate function.
Either toggle or hold can perform a wealth of functions (see drop-down menus from top of list to bottom) and assign (or keep unassigned) whatever function you need your footswitches to do.
For a 3 dB boost, I'd use a custom switch (located in factory layout 8) or build an external stand-in switch expressly for this purpose. The way to go about it with the external switch is to use a modifier on your amp's input gain toggle (in amp block > ideal), select either pedal 1, 2 or 3, as your input.
Here's how to use external switches with the FM9. I'll let someone more qualified handle this, it takes too long to write, and folks prefer watching videos instead...