I work in an environment with a variety of hardware, so we usually use automated installs and group policy instead of drive imaging for deployment of Windows 7. One step we always have to do manually is to open Windows Update and tell it to upgrade to Microsoft Update. How can I deploy Microsoft Update automatically?
WSUS does not really solve the question. It only is the location the computer will download the Windows Update patches from. Normal Windows Update takes it from the Internet, versus WSUS with is a local server with a cached copy of Window Update patches. That said, if you have a moderate to large environment, a WSUS server can really reduce Internet traffic.
Some general info about GP and WU: Group policy can tell client computers to download and install patches, when to do it, and to use that WSUS server instead of going to the Internet.
Open the Group Policy Management console and click on "Default Domain Policy". Under Computer Configuration, right click Windows Settings and click edit. If it tells you that it can't find gpedit.msc, copy c:\windows\system32\gpedit.msc to c:\windows\SysWOW64.
From there you go to Computer Configuration>Administrative Templates>Windows Components>Windows Update and make any changes you want. Do a gpupdate /force on any computer you want. To change the location to a WSUS server, configure the "Specify intranet Microsoft update service location" option.
As far as your specific question, there does not seem to be a GP option to force the use of Microsoft Update (all products) rather than just updating Windows. This is certainly because it is not configuring something already installed, but rather, you have to go install it. Whatever the solution, it would involve scripting involving running the download package if you can find it. I looked high and low with no luck. I will keep looking and update if I find it.