Visual Studio: Referencing the Same Assembly Multiple Times framework 3.5

At work I have the somewhat esoteric requirement of referencing multiple versions of the same assembly from a consuming assembly.

I change the alias of the reference from global to "XXX" and in the first line of my class  I put

extern alias xxx;

But it steel much an error :

extern alias 'xxx' had not specified in option /reference	

I even tried to use The C# compiler (csc.exe) has a /reference switch to
supply references that takes the following format (from MSDN):

/reference:[alias=]filename

follopwing this article :http://kentb.blogspot.com/2008/11/visual-studio-referencing-same-assembly.html

But i steel have the problem.

My project is in .Net 3.5 and VisualStudio 2010

thanks