How do I train my dog to sleep somewhere other than my bed?

This may not be possible, but I want to train my 6 year old doggie to sleep on his own. If I leave my bedroom door open, he comes and snuggles under the covers every nite. He will NOT go sleep in another room or in his crate by himself. I've let him sleep with me since he was a puppy (since he was housebroken ang big enough that I wouldn't roll over him in my sleep). I know I've created this problem but I need to know a way to train him to sleep on the floor or in another room without having to shut my bedroom door. If I shut the door he whines and scratches at it to get in and that keeps me awake. He's just a 12 lb babydog, but at this point I'd be teaching an old dog new tricks. He's not allowed in my bedroom when I'm not at home, I shut the door and he sleeps all day in an easy chair in the living room. Any advice?