Right. Get rid of the reflectors. In fact, change the handlebars for ones that are about a foot wide, while you're there. Wear skinny jeans, rolled up to your knees to avoid the chain. You'll need a courier bag, obviously, even if you haven't got anything in it. And, as you so rightly point out, helmets often look pants. Don't wear one. Wear a tweed cap.
Make sure not to wear anything bright. Blacks and dark blues are where it's at. Fluoro gear is for old men and geeks.
Oh, and chicks really dig it if you cycle whilst listening to your ipod.
I hope your bike doesn't have any gears.
Have fun.