For the love of God, is there an Nikon adapter that I can leave on the camera?!!!

[dUNIT]

I need (if it even exists) a Nikon adapter that I can leave on the 5D and be able to just switch lenses as if it was an F mount. A good example of what I'm talking about is in this video, which shows one like that, but for an M42 mount.

http://vimeo.com/3353663

Thanks in advance.