I asked this question a while back when the CK came out, but now that it's been a while I thought I'd stir the waters again and see what happens. I'm trying to figure out how to take existing exterior cells - mostly wilderness - and duplicate them in my own worldspace.

Specifically, I have a valley that already exists in Skyrim. I want to take that valley and "enclose" it into a huge cavern. The Tamriel worldspace part is easy - just wall up either side of the valley and insert entrance/exit links. But inside my cavern worldspace, how do I duplicate the valley that's in the Tamriel worldspace? I can't find a way to copy 30+ exterior cells in the CK, so I'm hoping there's some utility or tool that will help me. And I also realize that there's probably some LOD work involved, since ideally you would still be able to stand at one end of the valley and see the other end off in the distance.

I've found a couple of tutorials/forum posts about this topic on Oblivion & FO3 forums, but no definitive answer. I'm hoping it's doable and just not documented.

Thanks in advance to anyone who can help.

OK, what you want to do is make a small child world of Tamriel. And make sure to check the box that allows the child worldspace to use the parent's LOD.
scroll to the cell coordinates you want. And start building.

If you tell the child world to inherit the parent world's features then all will be well.
http://www.creationkit.com/Worldspace

Is that what you were looking for?