How do I install "Server-with-GUI" on a running "Infrastructure Server" environment?

I am running a virtual lab/dev environment with no Internet connectivity. I have many RHEL7 Server virtual machines, mostly built with the Infrastructure Server environment packages during install.

A few instances now require a GUI desktop. How can I easily install the Gnome3 Desktop (such as comes with the Server with GUI environment packages) without access to the RHSM network or repos, just the initial 7.2 Server DVD? I don't want to rebuild the VMs, I want to add the packages.

Packages groups don't seem to be working normally anymore, with 7. I know they do work in some cases, but not if I simply mount the DVD and create a .repo file that points to the DVD path. It finds the packages well enough, but no group definitions or info.

Are there a few key packages I can install that will invoke the proper dependencies and achieve the same affect? How do I identify them?