How do I pre-activate windows 7 for our customers?

Question

We are an oem system builder deploying windows 7 and 8.1 to our customers. The microsoft documentation suggests that we should be able to activate windows on their behalf as long as the machine is then sysprepped so the user is presented with the windows
welcome screen. 
Here is the text from the "how sysprep works" page at http://technet.microsoft.com/en-us/library/dd744512(v=ws.10).aspx
"Activating Windows Before Shipping to a Customer
Most customers can easily manage activation after receiving their computers. But if you prefer, you can activate the software on behalf of your customers, making it easier for them to start
using their new computers. After activation is completed, most users will not need to activate their installation again.
To activate Windows for your customer, use the unique Product Key from the certificate of authenticity (COA) label that is affixed to the specific computer, and activate the computer on
behalf of the end user. Run the sysprep /oobe command to prepare the computer for delivery to the customer."
In practice this is not working. I can activate the system in audit mode but after running sysprep /oobe /shutdown the product key is removed and the computer is no longer activated. I know
that a key can be stored in an unattend.xml file and used with sysprep but any of the solutions to do so indicate that the key should be entered in the specialize or generalize passes. Neither of these passes are processed after running sysprep /oobe /shutdown.
Sorry for the long winded post but I've been at this for a few days and I'm getting nowhere.

Answer 1

That should work if the answer file is used to install or if sysprep is run with /generalize. The specialize pass is not processed during oobe or on first boot. 
I attempted a test with an unnattend.xml file that has the oobeSystem and specialize passes. After oobe and after the computer starts this is what the unattend file looks like:
<?xml version='1.0' encoding='utf-8'?>
<unattend xmlns="urn:schemas-microsoft-com:unattend">
<settings pass="oobeSystem" wasPassProcessed="true">
</settings>
<settings pass="specialize">
<component name="Microsoft-Windows-Shell-Setup" processorArchitecture="x86" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<ProductKey>xxxxx-xxxxx-xxxxx-xxxxx-xxxxx</ProductKey>
</component>
</settings>
</unattend>
As you can see wasPassProcessed is set to true for the oobesystem pass but not for the specialize pass.
And of course the product key prompt is shown.