This may be totally off the wall and certainly not thought all the way through but... I was thinking about the idea that was suggested of getting a large group of people together to do something, and thought about those viral videos of the people doing a "freeze" in grand central station. Done by the group
ImprovEverywhere.
Now, they're in New York, but a spinoff site "the urban prankster network" has local groups for people interested in doing this sort of thing, and there is one for
Cleveland. It doesn't look like the members have actually done anything yet, but looks like there is interest, maybe you could recruit them for something?