Or a simpler low tech solution - just convert it to hand gear change?.
A friend of mine did just that in 1972 - following been 'wiped up' by a car in 1971 (he was in hospital for just under a year, with a very badly smashed leg).
When he came out his leg would hardly bend at all, so he fitted a sidecar on an Aerial 500 he had, and converted it to hand gear change. Simply saw the end off the foot change, drill a hole through the end, and pivot a steel rod through the hole. Run the rod up to the tank, and have a lever and pivot there, easy peasy
He also moved the footrest, as his leg didn't bend, to the front of the frame tube, and rested his leg on that.
The sidecar was basically for support, as to start the bike he had to kick start it with his left leg, while trying to balance on the damaged right leg, which was incredibly weak - so he had very little to stop a solo bike falling over. Once it started, he swung his left leg over, then reached down and lifted his right leg up onto the forward foot (leg) rest he'd made.
To continue the story, his leg got stronger, and he was able to start riding solo again - then while riding a Triumph Trident 750 he was wiped up by a car again, damaging the same leg. This time it wasn't so bad, and he didn't spend long in hospital, and once the break had healed he found he could bend his leg a great deal further than he could previously.
As for the Aerial 500, he converted it to a sidecar trials bike, and competed at a high level in the UK and Europe, the only person riding an English bike.