Used one of those "Renovator" style vibrating tools with a plastic-cutting blade on mine...good firm hand control is required during the surgery, but it was pretty easy - like a knife thru butter in fact! All done in about 10 minutes.
As the OP implies, it's a cheap and easy fix, and gets the main roof panel working properly again.

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Current:
2004 X5 4.8is - Le Mans blue/Cream beige
1994 E31 850CSi - Sterlingsilber

Previous:
1987 BMW E28 M5 - Delphin-metallic
1976 BMW E3 3.0Si - Arctic-metallic