One of the first things I put together before even taking delivery was a temp spare and BMW jack set that comes w/ a really cool pre-set torque wrench. I bought it to use on trips, but it comes in handy for things just like this as well.
Search in the wheel & tire section for the details. IIRC it's a spare wheel from an X6, a centering ring, a temp tire size from some Cadillac. Important thing is that it is the correct diameter for both F & R, and that it clears the front brakes. All the details, part #'s etc. are in the thread.
This is actually the first time I have ever used it & it worked perfectly.