I just change the SteamAppId from 218 (play ex normally) to 440 (map ex as 2009) in the gameinfo file in the ex directory.
No double versions, no complex crap just change that one identifier before i open it up. Had valve not borked the hell out of hammer not too long ago, it would not be a problem.
i know that way but....dont you hate to change this freakin file every time you want to make a map then test it or play EX
as one solid mod can make it all works with test and stuff
once again , its not belong the 2009 engine