I really appreciate your effort to try and help me. Unfortunately your pictures don't really show me the whole story. Without seeing exactly how the right hand side is wound, it doesn't really help me.
I've received some more belts of varying sizes from EBay now (all the way from Latvia!) so I think I'm going to have to try my 3-belt solution. Everything should still turn in the correct direction with this solution, so hopefully it should be ok.