Won last time I tried, so I guess it's worth another shot!
I build up high in the mountains, so I would order them to gather up in the Fun Room, order one to Pull The Leverô, and then they would all fall into this pit full of 1/7 water, save for a tile that descends into the depths. They fall in there, find themselves floundering in a sudden underground river current because that's actually where it goes, and it pushes them along off a waterfall into the lake outside the fortress, where they can then climb out. Fun times for everyone!
If I win, I'll take a copy of Minecraft, thanks.