I'd worry about the possibility that the wiring would cause unforseen interactions.

You can get multi-pole switches, but these tend to be for use in audio circuits and would probably not be robust enough for foot use.

If you are handy with a soldering iron you could build a box using CMOS switch chips such as http://www.fairchildsemi.com/ds/CD%2FCD4066BC.pdf to do the open / close operations for multiple electronically disconnected switches, using your "ordinary" foot switch as the control signal. You'd need to use a battery or psu to run the thing.