Okay, here's where it gets kinda tricky. the keys to a hidden door are the hinges have to be hidden. there are a couple ways to handle this, if you door will swing in, you can simply put the hinges on the back. I however wanted my door to swing out so the carbonite block can be seen as you open the door.
What I did was put the whole center bookshelf on wheels. I then mounted thread pipe floor flanges with threaded pipe inserted in them. I drilled a hole in the board I mounted accross the doorway and this allows the bookcase to swing in a fixed arc.