Hyper-V OS Deployment

We perform computer repairs and services, and have currently built a Win8 pc with Hyper-V that we have been using to create sysprep 'base images'.

Essentially, perform the Windows install on a VM, enter audit mode, install OEM info, drivers, Windows Updates etc. Snapshot the VM, sysprep /generalise /oobe, create the install wim from the VM that will be deployed on to the customer machine via DISM and then revert the VM to the snapshot state so the rearm count doesn't get used until the client machine boots up and enters OOBE.
The problem we are having now, the VM's have been installed longer than the grace period and as such, will not perform Windows updates. Is there anyway this system could be made to continue use without haveing to rebuild the VM's every couple of months due to rearm counter?

I know the of MDT, but that is built for use with Vol/KMS/MAK keys if I'm not mistaken. The method we are currently using allows us to have an up to date image for any os (currently only using 7/8) that can be quickly deployed to a customer computer with their existing Installation Key.