Forget the footswitch-activation idea (though it would be nice of course) -- all you need to do is grow a third arm (on the left for the PSR 2000). This arm could also serve other useful purposes, such as:
1) Changing volume with main volume knob
2) Scratching any itches that may arise during performance
3) Waving to the audience
4) Shooing away over-curious kids who wander too close to the keyboard
5) Eating, if the need and possiblity arise
6) Playing!