My recollection with copying user profiles was that you'll need to know the folder name. For instance, when I had a user profile for the local computer ("workgroup"), the folder name was C:\users\tonyf. Then I joined a domain and then signed in as a user on the doman whose name was the same as the local computer (domain user: domain\tonyf), then the folder name became C:\users\tonyf.DOMAIN. However the names might be different if you do it the other way round. For instance if I started out on the domain, the user profile folder would have still been C:\users\tonyf without the domain tacked on, and if I later switched to workgroup, there would have been another thing tacked on (perhaps the name of the local computer? Don't remember).

What I'd try is this:
- Create a local user account before even unjoining the computer.
- See if SYSDM.CPL lets you copy the Domain user profile on top of that local user account (you have to know the folder names correctly).
- See if you can sign in as that local user before you bother to unjoin the domain.
- See if the user account seems to work as-is and see if it seems to have correctly gotten the settings from the domain user. (it might not automatically sign you into domain resources but it should prompt you for creds at least).
- Then see if unjoining from the domain works, then see if that local user still works.

If that works, then my first post in this thread was a total lie, I actually did know how to do it.