Fastest way to update defs after deploying imaged computer

We finally included SEP 12.1 R3 in our latest desktop image build.  The clients are registering with the SEPM just fine because we ran the ClientSideClonePrepTool before taking the image.  The challenge now is as the virus definitions in the image get older, what is the fatest way to update the virus defs when setting up a new desktop?  Yes, I know the clients will eventually recieve updates from the SEPM (we have a 30 minute heartbeart) but looking for suggestions on the fastest way we can update defs and get the desktop re-packed and shipped out fast.  Thanks