Hey MC,
Take a look at
http://www.myapexparts.com/bmw-z4-m/ at the red ///M. The car has arc-8's 18x9.5 square setup but the ec-7's and arc-8's have the same offset so it's the same setup you're looking for. Now I'm not sure what suspension this guy is running but you might need spacers to clear the spring... We know it's possible though!