Ummmm... Sorry, its a bit late, but I guess its never too late for anything I had this in mind the day I read your post but somehow things turned out to be the way that I am posting this now.
What you see in these pics is a small brush, just like a bottle brush. Its primarily designed for cleaning baby feeder nipples and is easily available at general stores usually along a bigger brush for the feeder itself. Cost me 140rs for both, the bigger one is pretty useful for cleaning wheel wells, I've been using once since a year now.
I used to to clean a side vent of a city 2009 and it worked PERFECT. Though it was a bit time consuming and a little messy as the brush got dirty very frequently due to small size.
I used a normal shampoo solution for the purpose since the dirt isn't stuck fast, its runny, didn't need the plastic to show up dry without a cause.
Sorry I didn't take pics as my own blackberry's camera failed in the dark, i came home and borrowed someones phone for these photos.
P.S: Sorry for the corolla grill in a Honda thread I just wanted to show how it works and there weren't any citys around, if there is ANY confusion at all, just ask!