Re: crazy question about mesa footswitch???
I completely forgot that my Mark IV even HAD a footswitch until I ran across it the other day in the back of a closet. Ditching that switch and moving to midi for controlling the Mark IV functions was the first and possibly best move I did with mine. One footswitch push and everything happens: channel switching, effects processor patch changes, stomp boxes in/out of signal path...
So you might want to check into a basic midi pedal coupled with something like a Midi-Octopus, a Peavey Midi-Pro, a GCX, or any of the other midi devices that take in a midi signal, and operate multiple switching devices. If you're going to keep your Mark IV a long time, you won't regret it.