Falo got a reaction from Kevin Luck in integrate product key/serial #
There´s an option under "Main" and "Intermediate" tab called "Unattended Creator".
Here you will find what you are looking for.
When you have created the file and saved it, go to WIM Manager (also under "Intermediate"), load your image and
choose "Apply Unattended".
Choose your Unattended File and press "Full".
Hope this helps