Microsoft have just released a hotfix that allows the Windows Server Update Services (WSUS) role to be enabled. This hotfix and description is available here – http://support.microsoft.com/kb/2762663
Once the hotfix has been applied, you can then enable the WSUS role on a server running WS2012 Essentials. You can read more about how and what WSUS is from the Microsoft Technet article here – http://technet.microsoft.com/en-us/library/hh852345.aspx
A word of thanks to the HP Coffee Coaching Team, MVPs and IT Pro Community who have campaigned to have this feature enabled in WS2012 Essentials.