I have seen it done with a CRT g3 imac, I'm sure there is a way with the current generation. Definitely not without dismantling, and probably soldering. Its not hard with a G3.
I feel that this is something that should definitely be included. It would make the imac a lot more useful especially as they get bigger screens. If they end up with a 30" iMac, it would be great to use that screen for a variety of other products (laptop, console, HDDVD player, etc) instead of having to purchase a separate screen.