Spending a night on the Great Wall - call for fellow sleepyheads (Beijing)

I know there are a couple of travel agency offers out there, spending the night at Badaling for mind-boggling Protected content or so.

I'd like to do just that without the help of overpriced expat services.
A couple of wonderful people, food, some wine and sleeping bags and a beautiful, starry night on top of Huanghuacheng or Simatai.

Two questions: legally possible? And who'd be on?

Looking forward to hear from like-minded adventurers!

O.