firstname.lastname@example.orgWe have done this manually in the past for clients moving from a workgroup to a domain. If you check the registry key HKLM\Software\Microsoft\Windows NT\Current Version\ProfileList\ you will see an entry for each user. Each entry contains the location of the profile and the SID of the account. If you knew the SID of the AD account you could change this.
We manually log on as the AD user and let it create a profile, then go into the registry and change the path to point to the old profile.