Instrument DLL’s in the GAC

I’m trying to learn how to perform code coverage on my ressources in one of my projects. This project both have helper dll’s writen as normal c# classes and a orchestration dll. When I deploy my solution, all the ressources are places in the GAC.

My problem is know, that I don’t now how to instrument the dll’s when they are in the GAC?

I have tryed to use “vsinstr” on the local copy of the dll’s and the run VSPerfMon, but I just get an empty coverage data file, because the versions placed in the GAC is used?

Does anybody have a workaround for doing code coverage? 

/Anders