TFS 2012 - work items - validating area path

We need to restrict certain team project users, to be able to save WI's only to level 3 and below, in the Area Path Tree.

We found the following article from 2009 with a workaround suggestion, by creating a field named "area path validation", and defining a prohibited value on it. See attached http://blogs.msdn.com/b/teams_wit_tools/archive/2009/02/07/work-item-rules-workarounds-validating-area-path.aspx

Is there a simpler way to implement this in TFS 2012 (or TFS 2015) ? Thank you