The manual does state:

Notes: 1) You must use a stereo ¼” phone plug to connect Aux Switches.

 Bespeco does state its mono jack only but try this- enter the [AUX SWITCH] menu, change TIP- HOTSW   (not TIP+RING). now toggle the polarity switch until pressing down on the pedal engages the Hotswitch instead of letting it go. I believe you would still need a stereo cable for this but not positive about it.