It seems to me that you just need to photograph someone in front of any one colour screen that does not match any of the colours of the subjects outline and it would be a fairy easy job in Photoshop to put them into another backdrop.
I recently designed and built a virtual set for a TV science series for kids. The presenter is videoed in a green studio, and integrated with the set in post. http://www.larry-bolch.com/shade/set/
The producers are thinking about a much more interesting project in the near future that allows people to wander through a set - even behind virtual objects - which will be integrated in real-time. Evidently it allows quite unlimited camera angles, moving cameras and so on. I have heard that the hardware is now in place, but I have the feeling that the software may still be in development . There is a load of information on the hardware on the web-site, and considerable mention of the true 3D virtual set, but few details on how it works. I expect everyone will be learning as we go, once - and if - the project is confirmed.