Landscape might be of interest to you. This is the "official" management tool for managing large Ubuntu deployments, and Canonical is probably very keen to get your dollars for its use.
First, a disclaimer; I haven't used mirroring for Debian or Ubuntu, so I am not familiar with the software.
Second, it appears that apt-mirror would be "too heavy" a solution, my apologies. The original idea was that you would have a separate test machine (or test environment, probably a virtual machine?) to deploy the update on. Once you are satisfied with the performance of the update, you would pull/put the package into your "deploy" mirror (there would be the local mirror from the official sources, and a secondary mirror for just updates that you wish to deploy). The remote machines would then run an update at a pre-set time and pull it from your "deploy" mirror onto each machine, a cron job consisting of:
apt-get update && apt-get upgrade --quiet --assume-yes
Unfortunately, as I began to read through the details, it seems that
apt-mirror will pull all kinds of stuff and not just the packages you are after. So, I'm going to abandon this idea, although the concept has some merit.