What version(s) of Windows are you provisioning with your system package? I think I have some example, I'll look these up and confirm if they'll be helpful. In general we will supply detail as outlined by the Windows unattended install docs, but they can change between versions.
Windows 2008R2 and 2012
For Windows 2008 there is this reference list:
For Windows 2012 I did not find a specifically different set of documentation, so this may be the same. Let me know if you find this doesn't work with 2012 and we can do some further research.