Never done this, but I'd think this would work...
mount the vhd(x) and copy the contents of the profile directory to c:\users\<username>. I'd use "psexec -s -i powershell" to run powershell as the system account so you don't have to change any permissions on the folder to copy it. get the acl (get-acl) and store it to a variable so you can restore it after copying the content (set-acl). then in the user profile\appdata\local\fslogix - there will be a .reg file with the profile information - merge that
Would think you should be good to go after that