A little stretched is not a problem, the real problem to tell the truth is the ET40, I have doubt that fits, and the 9.5 inch rear wheels with ET45 too.
Making a research today, I found a store in UK that sells Beyern:
http://www.rimstyle.com/alloywheels/...ulti&year=2013
I made this because in Europe sites have F20 beyond the cars application, in US doesn't exist.
For this site, when we select a F20 and 18 staggered set that I looking for, they send together a 3mm spacer for rear wheels to better fit, maybe my doubt was answered here, if the site was right, I need a pair of 3mm spacers too.
Thank you, if somebody knows something more about this set and could help I will appreciate very much, is hard to find informations about the wheel fitment in F20.