I've done it to some old smoktech black ego batts that were really scratched up. Use a high-grit sandpaper, or a scotch brite pad, and spin the ego inside the pad. You want to make sure you do this pretty carefully and evenly to get a good uniform brushed look. If you have a drill with a chuck large enough to fit a carto, you could use the drill to spin it, which will make it easier to get a uniform look.
I'd be extra careful with the spinner though, as I wouldn't want all that dust and dirt getting inside the voltage dial at the bottom.