An alternative to dressing the tire is simply cleaning them really well. (requires moving the car back or forward to get all surfaces.) One thing that works is waterless hand cleaner (like GOJO or such). Of course, if you're going to use a gel-like cleaner such as this on tire treads, you'd better be really determined, and have a toothbrush, 'cause there are alot of angles to clean! You could, of course, also experiment with spray cleaners and a brush to see which one gives you the blackest/easiest to achieve acceptable results look. This is just a short term fix as well, though, as the treads will dirty up as soon as you drive on less than pristine roads (I know....not too many around, but I have heard tell of such places!).
One other alternative that may work, although I would obviously have no first-hand experience with it, would be doing something that I've heard called a "burn out". This seems to take the dirt off the tires fairly easily (now the effects on the paint...THAT's another story.) :naughty
