Hi Jackjordan,
I've tried this morning to use my Ernie Ball Pedal as second expression pedal.
You have to use a stereo cable Y (1 stereo into pod exp 2 in + 2 mono into in & out ernie ball).
I have only one problem: the value goes to 100% at half stroke. Maybe a ohm problem? or the taper switch which provides the user two distinct volume swell rates? Today I have no time, tomorrow I'll see..
Matteo