well, preventing from double click might be hard,
but after your page loaded you can get the text the inside of fb like box element, learn the id via firebug) if it is ‘liked’, you can hide the box..
of course you can do this only for fbml, not for iframe.
otherwise, you can’t!
i suggest you to check other likebox styles. http://developers.facebook.com/docs/reference/plugins/like-box
solved Facebook like button: How do I prevent people accidently “unliking” my page? [closed]