You will have to use complex .cordll commands to load the mscordacwks.dll explicitly, which is covered in this blog post,
http://blogs.msdn.com/b/asiatech/archive/2010/09/10/how-to-load-the-specified-mscordacwks-dll-for-managed-debugging-when-multiple-net-runtime-are-loaded-in-one-process.aspx