I couldn't see it being anything but a factory option. I can't imagine dealerships doing any kind of machining. I just don't think the tooling and/or training is going to be there.
Personally I'm going to sit on the sidelines for an F30 version of
http://store.vacmotorsports.com/vac-...als-p2324.aspx . Maybe if enough of us call they'll do the R&D
I've had
http://www.e90post.com/forums/showthread.php?t=365404 bookmarked for a while. It's missing some pics, but a very good writeup. This guy did his research and concluded Quaife.