Copy .cab files from "4th Generation>>640-640XL" folder and put them to D:\cabs (easier to access).
Put the Phone to Flash Mode again (Restart then Hold Volume + button)
Use Cmd.exe with the previlege and move to D:\ drive
Put the .cab file by:
iutool.exe -p -V D:\cabs and fire away (Enter). You can use the Tab key for auto completion for the typing.
After the last cab file successfully transferred, keep the phone plug in. The update started but did not show anything change on the cmd console. Wait for 20-30 minutes, you will see the Lumia start, now you can pull the phone off the cable.
After the phone restarted, the welcome screen is different. It asked to set up as a new phone or from a backup setup. Yay!, No key was asked.