I'm not sure if it's practical or not for your situation, but you could have your actor walk very slowly down the sidewalk while everybody else moves at real time... then in post you speed up the footage and add some effects that Eran Stern talks about in this tutorial.
http://library.creativecow.net/articles/stern_eran/Time_FX.php
The challenge would be for the actor to walk that slowly yet smoothly so it looks natural when sped up.
Mark Fogarty
Media Missionary
Muddy River Media
www.MuddyRiverMedia.org
