How to control Wah parameter on WahWah Effect?

I've been trying to figure out how to use an MK-449C keyboard with a bunch of assignable controllers to control the Wah parameter on my Sonitus WahWah effect. I have no trouble using Record Automation to record the movement of the Wah setting with the mouse, but how do I get a controller on my keyboard to control Wah? Right-clicking on the Wah knob does nothing, rather than let me choose a controller it should listen to.

Help! and Many thanks!!

-spinLock