What to do? I didn't want to ride it, because it would be a disaster waiting to happen. This wheel had an IGH, so there are no derailleurs on the bike.
I swapped in a spare road wheel, with a single sprocket from an old cassette (with some spacers as "packing") to make a home brew single speed.
... And I love it! I don't know why I waited so long to try single speed commuting. There are a few hills, and some grunting required, but it's great!
48/17 in case anyone wants to know...

