I was recently required to manage a number of clients in a workgroup with the WSUS server within my domain. In order to so, this is as simple as modifying the clients registry settings to replicate those of the clients within your domain, so basically you will be required to create/import the following registry key, HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate:
"TargetGroupEnabled"=dword:00000001 "TargetGroup"="Managed Workgroup" "ElevateNonAdmins"=dword:00000000 "WUServer"="http://wsus1.domain.com" "WUStatusServer"="http://wsus1.domain.com"
The above registry settings will configure your WSUS client to use a managed computer group on your WSUS Server with the name ‘Managed Workgroup’, where only the administrator can install updates and the Windows Update and Status Server is configured to be WSUS1.domain.com.
The additional automatic update options of the workgroup client can be created/imported to the following registry key, HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU:
"NoAutoUpdate"=dword:00000000 "AUOptions"=dword:00000003 "ScheduledInstallDay"=dword:00000000 "ScheduledInstallTime"=dword:00000011 "UseWUServer"=dword:00000001
These settings will enable automatic updates to automatically download and notify for install (I choose to install my approved updates on demand using WUInstall) every day at 17:00 and to use the Windows Update Server.
A full list of settings can be found at http://technet.microsoft.com/en-us/library/cc708449(v=ws.10).aspx.