As Zach said, it attaches itself. In the flange that inserts under the roof line, there are small slits, like a louver. They're supposed to bite into the underside of the roofline, but when the rail is removed, they usually cut that area away. I have had success with inserting a small screwdriver blade into them and opening them a little more. Some have added some spots of windshield setting tape or RTV to help hold it.
There is just 1 clip at the rear end of the drip rail. It's a steel clip that fits into the end of the drip rail and slips up underneath the flying buttress. The usual area where the rail comes loose is at the front tip, behind the mirror. If you can keep that part tucked in, the rest usually stays put, providing the clip is in place in the rear. That clip kind of rolls in, then the rail is inserted underneath the roofline, working toward the front.
That is for the Fastback. The Notchback attaches similarly, but I don't know how it terminates at the rear end.