Pirates Bight at Norman has a good dock and should be accessible.
Leverick would be another spot with a good dingy dock. Bitter end and Saba both have good docks.
We beached the dinghy at B-line
It might be easier to beach the dinghy and have him swing over and wade in.
Last trip we saw a young man in a wheel chair that was having a blast. His crew has a bosun chair set up to get him into the dinghy and they had the 4 arm ladder carry down pat. In and out of the dinghy no problem!!
I hope you have a wonderful trip