Yes, there's an excellent roof rack solution for the 335xi Gran Turismo. Yakima's high-end brand is called "Whispbar". Their system fits perfectly, is low-profile and has very little wind noise (hence the name, I guess).
I called Yakima, Thule and BMW, and all of them said that there wasn't a solution available yet for the 3-Series GT. Strange, for a car that's positioned as an active lifestyle vehicle.
I then called the guys at RackSolid, a specialty store in San Francisco. They sorted it out right away, and installed the entire system for me. Call them at (415) 543-7225 or
info@racksolid.com. They've got stores in Berkeley and Los Angeles as well, and I guess they can ship what you need to you.
I tried to attach a few photos of the end product, but somehow I can't upload them at the moment.