If you look at either of the following keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\hivelist
You can find a list of the SIDs there with various values, including where their “home paths” which includes their usernames.
I’m not sure how dependable this is and I wouldn’t recommend messing about with this unless you’re really sure what you’re doing.