One of the news in Hyper-V 2012 R2 is Automatic Virtual Machine Activation (AVMA), which lets you install virtual machines on a properly activated Windows server (running Windows Server 2012 R2 Datacenter) without having to manage product keys for each individual virtual machine. It works even in disconnected Environments. AVMA binds the virtual machine activation to the licensed virtualization server and activates the virtual machine (running Windows Server 2012 R2 Datacenter, Standard or Essential) when it starts. Real-time reporting and tracking data is available on the virtualization server.
AVMA is easy to implement, use one of the following AVMA keys when installing a new virtual machine in Hyper-V:
More information is available on Technet: http://technet.microsoft.com/en-us/library/dn303421.aspx