How to use the FBV shortboard expression pedal for the bender?

[FAchterberg 0]

I own the Amplifi TT. Following the effects manual you can use the expression pedal from the fbv shortboard mkii as expression pedal to control the bender like a whammy. But how?

[Jaguar9080 16]

You can't. It doesn't work despite what the manual says.

 

The expression pedal only controls the volume/wah. External expression pedals don't work either.