I created a question on behalf of a non-AU user. Now they've signed up for AU. Can I make them the owner of the question, and if so, how? If not, what's the closest alternative?
Omnipotent as we are (or more accurately: aren't), even your moderators don't appear to be able to switch the user of a post. You could write to the StackExchange team (link at the bottom of the page) and they might be able to do it.
The simplest way would just to be to ask your friend to repost and then flag your old one for deletion. If your version has attracted answers before this happens we can merge the answers across.