WUInstall. The free version can be found at http://wuinstall.com/index.php/en/free.
I just tried this out on a couple of machines to see how it worked out. The WSUS patches were downloaded quickly and were installed without issue. Especially nice was it not rebooting the systems once the patches were done even though the patches required reboots for them to finish installing.
I do have one gripe about the free version – I would like to see the "show_progress" switch be functional if no other reason than to be able to confirm that a patch is progressing and not just stuck forever.
All in all, for a quick and dirty install patch automater I’m not going to complain too much. It sure beats clicking the windows update client, clicking custom, etc, etc, etc…