Haven't posted much on this site, but I have come up with a pretty good way to clean and polish the fins on my bike. I use foam paintbrushes. They fit snug between the fins and do pretty good job of polishing them up. You will need to find the better quality foam brushes that have a good dense foam and a sturdy plastic insert inside. You can pretty much rub like hell and not worry about screw driver or stick breaking through the material and scratching the shit out of your bike.
It probably won't shine it like machine polishing with the dremel, but at least you don't have to worry about burning in divits or the machine binding up and flying god knows where.