I love the colditz idea, i have a thing for castles anyway.
I think to make the lifeline thing work we could divide the area (twinwoods would be perfect) into zones; occupied europe, frontline, blighty/liberated europe.
Theres a nice long stretch of road with buildings, woods, etc.
The Germans can setup their zone, we can have some civilians there, perhaps a building?
The road could be free-for-all, thats where the visitors walk and reenactors who just want to look around.
So at the beginning our aircrew would walk down the main road into the German zone, there they will climb over or under the pallisade/fence and from then on the story will start.
Perhaps we can have a airraid siren go off so the germans and civilians know a aircrew has just bailed out.
We would need more then just one civilian though, otherwise the germans will know exactly when a airman is being smuggled passed!
This would be a great exercise for our SOE project