Hey man, I love this! But it has it's pros and cons.
It's VERY effective. I never had mine "ask" to be a part of the group as we always assign groups, regardless.
You can't have one. You need 5. If you have a line (I pray you do) they'll catch on if its the same face.
You HAVE to do it early on, and end it early on. You wait too long and you'll interfere with other groups or it'll be a dead scare.
A great way to integrate your planted actors is by having them use a VIP line, this way you can grab them as a single VIP and add them to your regular ticket line.
If you have a long line, it's impossible to pull off successfully. But if you're a starting haunt and only do a couple hundred people per night, than its doable.