You do know how that whole green screen thing works? The green color (be it the person or the background) is there so that a clean "background plate". But that background plate has to be gotten from somewhere. If you're shooting from behind the girl, you'd be (partially) be able to achieve what you want, but as soon as you're filming from behind the (invisible) guy, everything the guy blocks would be replaced by the background, e.g. the couch or bed.

