There are pedals that you can program to send sys-ex when pressed, but are you sure you can't call up variations and other things with PC/32/00 commands? I know most of Roland's style divisions can be called up with those. And I think Korg do the same.

Can you point me to a document that details these codes? (I looked in the main S950 manual, couldn't find them)

And, if you CAN'T use simpler, easier to program codes, I'd sure get on Yamaha's case about getting it!