I know this thread is kind of...well, dead. But really, it sounds like it's being made a bit more complicated than it needs to be.
Why not run it like one of those pub crawls that's always happening? Obviously not alcohol related, because some people are under aged. But this would be something fun to do in the months leading up to the next con, perhaps in the summer. No venue needed. Meet up somewhere central, like Pioneer Square then move on to the park blocks. Just set out a block of a few hours, no formal structure needed. Just having fun. It also presents a nice opportunity to test out new cosplay before the big event.
If people would be interested in running it like that (pre-con, freeform fun), I wouldn't mind leading the way....which being leader fits in quite nicely with the costume I'm putting together.
Obviously, if there's interest in that vein, I'd set up a thread in a different forum since this one is more panel oriented....