i gotta agree with andy.
i think that pretty much any mod/admin/even community work towards an event like this will be completely lost, unless there is some kind of reward that can only be achieved by doing the event, or something worth their time (tbt shop items, maybe? i dunno.)
the pokemon league is a good example, since because the badges are all user-created, they are easily stolen and used in people's signatures to the same extent as a "real" winner.
if there was a solution similar to how the cakes appear on the user's profiles, then that's solved, move on. but we need some kinda support from admins and stuff.