thats a tricky one,how about playing spooky music as the trick or treaters come up your path,i done that a few years ago it frightened the hell out of them!!
Heh, I'm sorry but I just couldn't help it.LOL I don't know - it might be just me - but I think a slightly more descriptive answer was sought.....
I did the same thing in my 2010 haunt with great results. I had 7 body bags hanging in a zig-zaging room with a strobe. AWSOME resultsYou mentioned using body bags. In my haunt, I had 6 body bags, staggered down a hallway (I hope to add 2 more this year). It is the part of my haunt that scares people most BEFORE they even go through them. Many won't. Just to keep it fresh last year I added a little touch that no one was expecting. In addition to having my victim's arms or hands poking out of the bags, I hung a couple of heads in the midst of the bags, about face level. Imagine the ToTs surprise when they came face to face with that. The strobe light is a great idea. It keeps my ToTs from being able to clearly see to the other end of the body bag hallway, and also gives the bags a crazy flashing effect when they swing back and forth.
I love your asylum idea. I hope it comes out great.