I saw this, and was really smug because for the first time EVER in the history of me watching it I worked out (a bit of) the mystery. From the beginning I'd guessed it was a double roof!
The room in question either has a double ceiling or double floor. By first putting it into double floor position you can put any old skeleton you happen to have lying around onto it. Probably not that hard to obtain if you work in the film industry. Once you've done that, you raise it into the double ceiling position in preparation for your trick. You put your person onto the normal floor, leave the room, then lower the ceiling bit with skeleton on.
Hope that makes sense. In a moment of supreme smugness, I also knew she had to have a child no-one knew about out there. I thought it would be one of the two American actors.
I'm not sure if it was deliberate to leave a few more clues than normal to the mystery, or if after a few days of drinking I'd just killed of my inefficient brain cells so was cleverer than normal. I think it's better if you can speculate at least a bit one what happened. It's more fun.
