I made a footswitch to act as an expression pedal on my Tech21 Midi Mongoose. You simply need to put a 10k resistance in parallel between tip and sleeve.
A momentary switch will activates when you press and deactivates when you release.
A latching switch will actives when you press but you would have to press again to deactivate.
So if you change preset, you will have to press twice (to deactivate and reactivate).
Not ideal but working.