A chap called Steve Hahn plays the Stick simultaneously with the trumpet, and does it well. The trumpet is in a rig of course, and he's invented a pedal system for controlling the valves.
Me, as a renowned multi-instrumentalist, I've been known to play a Moog with my left hand and an ARP with my right hand. No less!
Seriously though, I've not had double roles, with one exception where my feet played organ pedals, my right hand synth or el.piano, and my left hand the flute. Of course the flute parts were specially written for this to work, and my sister played the other flute parts with two hands.
best,
bert