What is the best way to update the Nether for 1.1?

Much of my nether has been built in, and my players don't want to lose what we currently have. However, so much of it has been explored, and my players are having a difficult time finding new content. Is there a way to trim explored territory, while leaving the structures intact?

Well, I ended up using MCEdit, and simply cropping out all the chunks that weren't being used. Amazingly enough, the terrain generator must not have changed, because there are no noticeable sliced chunks this time around!! We already found a new fortress just outside of the cropped area.

EDIT by Moderator: merged posts, please use the edit button instead of double posting.