I replaced the OD switch with a 3PDT and use the additional poles to switch a stompbox into the signal path.

I also added an additional external DPDT relay (with its coil in parallel with the internal OD relay) This relay selects one of two effects loops; one for the clean mode and one for the OD mode. This allows a dedicated effects loop for each mode without having to step on multiple switches.
By adding the pole to the footswitch and the external loop switcher, I can have a stompbox (or several) and a rack processor switched in automatically when I step on the OD switch. When I turn off the OD the stompbox is out of the circuit and the clean effects loop is selected. This works really well playing live.
I have attached a photo of the loop switcher.

Well...each toggle switch (rock-jazz, bright, etc) can be replaced with a relay, I don't think there any simpler way to remote those functions. The power supply that runs the two onboard relays will probably handle a couple more. (I have it running one additional one now). There is also some power supply dedicated to the FET preamp which many people never use...you could re-purpose that if you need more.
As far as connectors goes, a good option is the XLR type. Neutrix makes them with 6 conductors (NC6MP). I think some of us have replaced the DIN connector with those.
Nik (or maybe somebody else) could tell us how much current is available from the regulator that runs the onboard relays...