Depends what brakes you have on the car. If you have the larger brakes (in the M suspension option) they won't fit over the caliper size. If you are just looking for a simple $hit I got a flat and need to get this thing to a tire place then a BMW spare wil fit. Realize the offset will be wrong. The other possible problem is how the rear diff will handle the different size (diameter) tires... I don't know if something will "burn-out" like what would happen on early 90's mustangs.
Best thing to carry is a $5 plug kit and a $15 2V tire pump. They are much smaller as easy to do as a tire swap and your can get on with life
... DO NOT use the "fix-a-flat" in a can stuff, it makes a mess and throws off the balance.