I'm sure a couple of forum members have fitted E53 X3 Style 65 Tiger Claw wheels to their Z4s, but given they are 9J x 19 fronts and 10J x 19 rears you might get rubbing issues.
TBF if they have winter tyres but you'd need to replace them to fit it would probably be much easier and cheaper to find a set of E46, E9* or E89 wheels with winters that would bolt straight on as 19" winters won't be cheap!
If you can wait a few months I'd let my skanky 17" Style 158 wheels with winters got for far less than that because I'm getting to the age when I find swapping wheels twice a year too much aggravation. So I might just replace my summers with Cross Climates.