If you look for more tips about modifying / using a bicycle with a below elbow amputation, check links regarding "bike" (LINK), "biking" (LINK), and "bike mods" (LINK). There is a longer article in German regarding bicycle modification (LINK).
My bicycle modifications were installed by the tech wiz bike shop CYCLE SHARK in Zuerich. They took time and knowhow and could have taken this even further. I required gear switch modifications. And they threw in an arm rest.
I now switch the rear wheel with a grip shift.
The front wheel is switched with an "old" 3-way lever without snap positions.
From an aerobar (Zeitfahrlenker), the arm rest was used to allow me to at least temporarily stabilize the handlebar or rest my stump.
The overall result is very functional and useful.