windows 7 - Retrieving OEM-SLP key from OEM Recovery DVD

I have a number of HP ProDesk 600 G1. I use Windows Deployment Server (WDS) to deploy a custom image to these machines (effectively removing HP bloatware) and I'm trying to find the OEM-SLP key.

I have the HP supplied Windows 7 Pro recovery DVD and managed to find the HP Cert file at DVD:\sources\$OEM$\$$\system32\OEM\oem-cert.xrm-ms.xml.

I've installed the certificate using slmgr.vbs /ilc oem-cert.xrm-ms which worked fine, however Windows still requires a product key to fully activate.

I was hoping that somebody here could tell me where I could retrieve the OEM-SLP key from the HP Windows 7 Recovery DVD please? I'm not even sure where to look..

Thanks

EDIT: I have already mounted sources\boot.wim & sources\install.wim to a local directory in hopes that the key may be stored in these.