For those following the previous multi-gear unicycle discussions, the issue of reverse torque transmission comes up because all bicycle hubs intrinsically freewheel backwards (with the exception of the S3X), making them incompatible with a unicycle drive.
The idea for solving this on the nuvinci was to install a 1-way ball bearing to lock the hub in reverse with a 1:1 gear ratio. So going forwards it has variable gearing through the CVT tranmission, while going backwards it is locked 1:1 with the sprague clutch.
To do this I first had to machine the Nuvinci hub down to size a bit in order to have flat reference surfaces for attaching a new side cover plate that accepts the 1-way bearing. Also took off the spoke flanges which aren't necessary in a jackshaft application.