Thanks, I wondered what that did.
Someone over at thegearpage.net said he uses a momentary switch plugged into the expression pedal port. I tried that today and it works like a charm!
I suppose it very similar to what you suggest. The advantage of using the pedal input is that it takes a simple T-R (mono) plug and I can use a simple, small, light plastic keyboard sustain pedal instead of the large metal 3-button momentary switch I have (the "J3" that came with my Johnson/Digitech Amp), less size and weight for fly-away gigs and less pedalboard real estate. I'll probably also set up your suggested method and use the J3 for home gigs.
Now, if only the on-board FLEX/LEARN switch could be made to function like the AUX PDL. I wouldn't need anything external.