If you're using the FBV 3, or the FBV Shortboard MKII with the Spider V series, you have the option of utilizing an external expression pedal. The external pedal would be plugged into the EXP Pedal jack on the FBV. This is how they interact with the Spider V's patches.
On patches without tweak assign to pedal, the external pedal becomes volume, the on-board pedal controls wah position, and toe switch toggles wah bypass.
On patches with tweak assigned to pedal, the external pedal controls the tweak-assigned parameter. The on-board pedal controls volume and wah, and the toe switch toggles between wah and volume control.