Caller Able to Dial while Parked

I’ve figured out many things thanks to this forum, and others just by searching, but I haven’t found a clear answer on this topic.

I’d like to give our incoming callers the ability to at leave the parking lot by dialing like 0 to return to the operator if they have been sitting there for a while. I’ve tried a couple of things but didn’t do what I thought they might. Maybe I am just missing something really simple, but at this point probably better to ask the experts so to speak.

Running Asterisk 1.8.7 at the moment.

What are the two things you have already tried?