I dont have a disabled duck but I have a chicken with messed up toes on both feet so she has trouble roosting and getting up big ramps. I had to modify her living situation a bit and she is doing well although she is definitely not doing as well as I'd like. I am trying to stay positive about her but I also suspect she has some reproductive issues and so might cull her this summer. If you think he is happy then I see no reason not to keep trying.