If you just want a black line and don't want the rough edge look, just pick up an 8055 carrier from Ebay or somewhere.

If you want to mod your current carrier (I would recommend buying another to work on - 8053 is the number), use a file or dremel tool. Someone recommended at one point using a six inch mill bastard file and sandpaper. After filing the carrier, go from coarse to fine sandpaper. I ended on 600 grit I think, though you could go down finer if you really wanted to. Once finished, I'd put in a scrap piece of film and move it around some to make sure you don't get any scratches.