Ah right, I'm not used to dealing with spacers which aren't 15MM+ , those generally have their own new centre hub lip.
Is it actually unsafe to run a car with the wheels bolted on but not located on the hub lip? I didn't think it was. I thought it was mainly just to help locate the wheel until the bolts are torqued up. Hence adapter spigot rings generally just being made of plastic.
No idea really but it is not something I wish to try especially in a car that I drive to and beyond the limits pretty much every time I drive it.