PX-575R - Leslie effect

[Subito Piano]

Hi! I recently picked up a PX-575R. Playing with the organs and editing the effects, I noticed that I can adjust the Leslie effect by changing the number value while playing and it will ramp up and down correctly -- quickly (but NOT instantly) increasing to fast rotation and more gradually returning to a slow rotation, just like a real Leslie cabinet. Does anyone know of a way to do this with the touch of a button or even how to reprogram the sostenuto jack to control this? (My church's Kurzweil PC2x does this very thing.) It is rather awkward to do this from the numeric keypad.

Thanks!