I have tried http://msdn.microsoft.com/en-US/library/ms228759(v=vs.90).aspx but I only get VS starting with a message box : Command "MyAddin.Connect.MyAddin" is not valid
"C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\devenv.exe" "D:\Projects\MyAddin1\MyAddin1.sln" /command MyAddin.Connect.MyAddin
Mark Latham