Here is what I would do.
1. Leave all forms of currancy at home, wallet, checks, credit cards, debit cards ect...
2. Make a cheat sheet or memorize the answers for the personality test from this here http://www.xenu.net/archive/oca/
3. Dress extremely casually, Shorts, T-shirt, and running shoes.
Go and take the stress test, either on the street or in the org, answering all the questions as they are exactly on http://www.xenu.net/archive/oca/
Watch them still try to reg you using your 'ruin'. It is fun to see really.
Methods of escape.
1. Not suggested, but extremely funny, interrupt the ruin interview by asking if $cientologist really believe they are infested with dead space aliens who were blown up in non-existant volcanos, here on earth 750 trillon years ago by the evil overlord Xenu. (Before doing this make sure you have a clear path to the exit. If the 'interviewer' gets up to get you an answer leave immediately)
2. Tell them your ruin is that you just declared bankrupcy and lost everything, your house, your car, ect... and that you are living with your father/mother who is a clinical psychologist. Don't worry about the exit being clear with this one, they will escort you to the door. If they don't, remember why you are wearing running shoes and casual cloths...
Well try it out, remember, the time they waste trying to reg you, is time they won't be regging someone else, you may also plant the seed of doubt in one of the members.