I'm not sure if your Haunt is big enough for this to work.
Old haunt we used to do, actually haunted an entire block of old victorian, decrepid houses next to a local Fort. This one:
We literally had thousands come through each night. Lined up six deep for over three blocks, so the following trick was easy.
One of the carnel rules was, "No Touching the Victims..er...Customers".
There was one little 7 year old actor, Jennifer, who could scream all night long. Her only costume? Street clothes.
We ran guest through the haunt in groups of ten. Occasionally, Jennifer would sneak into a group, where others thought she was a paying customer. About 3/4's of the way through the haunt, during the Graveyard Tour, a Big Ugly Werewolf (ME) would pick her up and run off with her screaming all the way. Scare the bejeebuz out of them.
I miss this haunt, but unfortunatly we lost the venue because they redeveloped the structures...great for the structures..bad for the haunt.