There is no need for a how-to. When you install Win 2012 R2 Standard or Datacenter in a Hyper-V virtual machine, simply use the AVMA product key from the linked Technet article, instead of a regular product key. If the host is running a legitimately activated Win 2012 R2 Standard or Datacenter, then the guest will be automagically activated.
Only 7 days? It's funny that trying to activate online a host with this keys, gives me "Windows is not been executed on a compatible Microsoft Hyper-V virtual plataform" error instead of telling me that I don't have internet connection Maybe some activation guru can do something with this.
I'd just like to point out that the AVMA keys only work on Datacenter. And not on Standard or Essentials. It maybe why some of you are have problems.
my host is win2012r2 datacenter tested in hyper-v with AVMA keys on datacenter standard and Essentials and it activated With this keys thanks for this info