Possibly similar arrangement as say a Lambretta scooter.
Spinning drum with non rotating shoes.
Got a works manual for (my) Lammy 150GP but the pictures are poor too blackened.
Welcome to peruse.
Bolting on a plate with slots for a drive dog like that is probably the best way. The only other way is a spider washer on the end over splines or a square or similar and going between the hub's outer holes like a reversed knock-off for wire wheels on a car.
With the above the driveshaft is shaped to fit and pass through the hole or put simply a 12mm solid shaft will be machined near the end to pass that hole. That hole will have a max width at the lugs no wider than the 12mm bolt that normally passes through. When the wheel goes on the piece of the shaft that fits the hole will end flush or just short of protruding and will then be threaded for a bolt. The only problem with this is owning the machinery to make the shaft and hole. Making something similar without that machinery would be a tough job. Probably easier to make drawings and pay a machine shop to make them.
The interesting bit is what he did to the inside of the hub to get this to work.
these hubs are hard enough to get to work normally as the mounting for the back plate is almost non-existent and cause me all sorts of problems trying to get them to consistently mount the same and so work without drag.
Sorry @stormbird, I'm just now seeing this thread. You may have already seen my planning sketch that I posted in your other thread. I think this sketch should answer most of your questions.
The butting of the grooves was a bit tricky. I don't have a pusher either. I made do with the height adjustment on my milling machine.