I tried everything suggested in this thread to no avail. My hands were killing me, I broke a screwdriver, and the gills barely even moved. Being scared to death of damaging the body or paint, I went a different route.
I jacked the front of the car up, and proceeded to spend hours removing the fender liners in order to gain access (very limited) to the inside of the gills so I could push on them from the back side to get them to come out.
All in all, I like the look of the car with the black gills but knowing the effort it took to make this minor modification, I simply would not go through this. I love working on my car but this was the least fun I have every had while modifying.
2008 AW E90 M3 - current
2002 TIAG E46 M3 - gone
1991 DiamondSchwartz E30 M3 - gone but not forgotten