After a few days of struggling, I finally got my Mooer Expline to work as a single expression pedal. I'm using a standard mono patch cable (unlike with Ocean Machine, used a TRS cable with that one) connected to the right side connector, and had to select the inverted tip polarity in HX Stomp (Global Settings --> Preferences --> Tip Polarity --> Inverted).
Afaik, this is the most one can do with the Expline, as it doesn't have a switch. Please correct me if I'm wrong!