ORIGINAL: w8ye
A Dremel is bad about getting away from you and dribbling across the surface of the cowl so you need to use cutters that are not so aggressive as these other people have suggested.
The best way to avoid dribbling across the surface is to note the rotation of the dremel cutting wheel, and not cut with rotation pulling up, but rather so it pulls the rotating wheel down. Cut less than the outline, leaves room for the sanding drum to remove the frays.