ConfigurationManager.OpenExeConfiguration - loads the wrong file?

I have added multiple app.config (each with a differet name) files to a project, and set them to copy to the output directory on each build.

I try and access the contents of each file using this:

System.Configuration.Configuration o = ConfigurationManager.OpenExeConfiguration(@"app1.config");

The code runs, but o.HasFile ends up False, and o.FilePath ends up "app1.config.config". If I change to code:

System.Configuration.Configuration o = ConfigurationManager.OpenExeConfiguration(@"app1");

Then the code bombs with "An error occurred loading a configuration file: The parameter 'exePath' is invalid. Parameter name: exePath".

If I copy/paste the config file (so I end up with app1.config and app1.config.config) then the code runs fine, however, I posit this is not a good solution. My question is thus: how can I use ConfigurationManager.OpenExeConfiguration to load a config file corretly?

I can't remember where I found this solution but here is how I managed to load a specific exe configuration file:

ExeConfigurationFileMap map = new ExeConfigurationFileMap { ExeConfigFilename = "EXECONFIG_PATH" };
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);

According to http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/3943ec30-8be5-4f12-9667-3b812f711fc9 the parameter is the location of an exe, and the method then looks for the config corresponding to that exe (I guess the parameter name of exePath makes sense now!).