So basically put on an extra seat in the middle, and make the pedals 2x wider, by attaching the u-profiles and glueing on some sandpaper for grip I guess.
I found a thread about tandem unicycles:
Would the suggested Microtandem count as a proper tandem unicycle?
It sure looks cozy… If one just grabs the handlebars and let the Backseat treat this as a MuniPacking trip… Ha!
Also, I can’t imagine how you should be able to (free)mount such a thing. The back seat must do the mounting. How will the pedal extensions even hold up?