Not often I see them but we have a Handicapped Tandem club in our area. All sorts of injurys amongst the stokers but several have severe balance problems. I Was asked to take my Tandem down once for an Extra rider and I was lucky in that I had an experienced stoker.I can still remember one of the teams and it was a Father and son. Son was about 18 and "Not" on the light side. The son had a balance problem ----- Off the bike. He was wheelchair bound but sit him on a saddle with handlebars to balance with and he was fine.
Only problem came about on stopping but they had got into a routine in that the son would stay as still as he could and they would always try to stop where the son could put his foot on a kerb- or wall. But he would not take his feet off the pedals till the Tandem had stopped.
They had come to a system that worked for them and it did. In the 5 miles of frequent stops in town till we got onto the open roads the balance problem did not show.
It had taken just a few rides to find a system that worked for them so hopefully you can too.
__________________
How long was I in the army? Five foot seven.
Spike Milligan