ones I have seen are designed to be held in place between the tubes rather than attaching as you illustrate. If it was just the steering it's relatively simple but then you need the controls..........
as a bad back man I would avoid any of this as 1. being hunched over and 2. bounced around whilst hunched over, are not high on my list. Sitting nicely upright on the seat with the tiller beside me does it for me!