I don't know about BMW, but if you bought winter wheels from Volvo then they store them for you, and change them over and then store the summer wheels.
Ah. I think kwikfit etc do the same, for a price obviously
My winter tyres are a different size to the summer tyres, and are therefore on a different set of rims - which is a bit of a bugger for storage as I don't know anywhere that'll stash them other than traditional storage places.
I don't know about BMW, but if you bought winter wheels from Volvo then they store them for you, and change them over and then store the summer wheels.