Lol, us amps prefer the term "residual"...but whatever.
I might suggest looking back through this sub forum as there were some discussions between myself and an AKA where he posted some pics of a system he created for his bike. I recall it being much like a "ladder hook" that was flat, mounted to the top tube.
In my own experience it is a good thing to adapt a prosthesis and crank/pedal/shoe setup to allow at least some way to use the amp side leg. Riding a bike without using one leg is going to lead to sacroiliac disfunction and pain in the hip, lower back, and so forth. It is also of note that riding with only one "leg" is fraught with dangers related to stopping, dismounting, etc. Another aspect to consider (unfortunately) is related to the possibility of a crash. A prosthesis will offer some level of protection to the residual limb. I PROMISE that striking the end of your limb even in a walking fall is insanely painful. Doing so at speed is in my mind, nearly unimaginable.