You could always have some kind of party. I'm not sure how many costumes there are out there, maybee a few from the other festivles, or an orb of deception. If I rember right every city has a bobing for apple tub. get a few folks with that stupid dancing trinket. maybee bring a kids along(low level alts) and pass out candy.
If you wanted to do something beyond the Clan we could make a post on some of the RP boards and let other clans know. tell them that anyone between level 5-25 or something is welcome to come and trick or treat for some candy, and everyone else is welcome to come and party.