Here is a reply from James at Sonoruus about using it as a volume pedal and independent expression controller
It's not currently possible to use the Wahoo as a volume pedal. In a future update, it would be possible to add this, but it wouldn't be a perfectly smooth volume control. The volume circuity wasn't designed for smooth volume changes, so although it can be controlled, it may have some small steps to it. Also, it can't be turned fully off, so you can't fade to/from complete silence.
The Wahoo's expression output (via USB-MIDI) can be used to control other devices or plug-ins so you could use those to control volume and thus use the Wahoo as a volume controller. So, that's an alternative solution, though admittedly not a self-contained one. The Wahoo expression output uses the full 14-bits available for MIDI expression, so you can get good smooth control with it.