I also agree that we should do it on VATSIM. Perhaps they'd be willing to "shut down" a particular airport in order to accomodate the show.
It's not likely that they would close down the airport just for us, after all, Heathrow is one of the worlds busiest airports and shutting it down could cause a lot of confusion. Plus, to use vatsim you need squawk Box. As far as I know it generates AI traffic a well so mabye we are better off using FS Host