Windows 10 Note
Windows 10 Update 1511 Seemed to bork at around 83%. I reverted it and found the profile had lost the start menu icons and was having lots of issues. This may or may not have been related to this method but I suspect it was. The solution was to copy the Users folder back to drive C, perform the upgrade and then move it all again.Procedure
Copy the files with:-
robocopy /copyall /mir /xj C:\Users D:\Users
Delete the old users folder (or rename it for safekeeping) And make the symlink (junction) :-
mklink /J C:\Users D:\UsersIf the drive mapping is different in the non-os booted system create a hanging link that will map correctly when the 'real' OS is booted. Update: Seems to work OK with Windows 10 but see the above caveat.