Changing environment setting in Add In does not update the current environment

In Visual Studio 2008 we use an AddIn that changes the environment during loading of a solution file, based on a text (environment) file.

This gives us maximum flexibility to switch between libraries/release locations/version numbers etc. during development.

This works fine on VS2008, but the AddIn does not work under VS201x.

I understand that the environment can not be update after the application is loaded (All tough the AddIn works fine under VS2008). The environment settings shows up nicely in the Visual Studio Command Line, since that inherits the environment settings made by the add in. 

I rewrote the AddIn with VS2013 as a visual studio package. Which didn't help much.

Is there a way to cope with this problem?

Rewritting all our project files and our 'environment' files (hundreds of them) is not really an option.

Kind Regards

Wai-Ming