I don't have the answers, but maybe I can give you places to look:
3rd party software might be able to do this. Look more into haxie stuff than anything else, but look around at it all. Somewhere, somebody has to be wanting this. Maybe if you pester the people at Unsanity, they'll get on it for ya
Interface Builder. This comes with the free Developer Tools from Apple. You might be able to find the window you want and change some property somewhere to make it float. I don't know if it would be easy, and I'm sure it would get tedious if you wanted to do it to more than a couple windows or if you want to be able to turn it on/off... but it'd be a place to look.
This would be a very useful feature to be build right into the OS... you should pester Apple through their feedback form
Good luck finding a solution!