Took the Z for a new rear at a mate's tyre depot and asked him about this again and he said it's a rim similar to a metal ring that goes roand a barrel that goes round the rim so that the tyre sits on this instead of the alloy. At tyre change time the fitter prizes the tyre off the rim protector with it protecting the wheel. He said the gear to fit these would mean him whacking £100 on extra due to the limited demand.
Normally he said if he changes the tyre with the wheel "upside down" so the face sits on the "machine" with the plastic protectors on, even if it's a bugger of a job, worst case he may mark the back of the wheel whilst keeping the face pristine.
He didn't say where to go for these though as he only heard about these at a trade fair.