It's possible to use an expression pedal and a one button aux switch at the same time. This page describes how to do that:
https://www.eventideaudio.com/support/downloads/using-both-aux-switch-and-expression-pedal-h9
Keep in mind though that this might not work with the expression pedal you already own; in our testing we found a great deal of variability in how different expression pedals work. So, if you consider that you might have to buy a new expression pedal and an aux switch to do this, it might make more sense financially to buy a MIDI pedal.
