[Twisted-Python] How to configure setup.py for a twistd TAP app

I want to deploy my Twisted app as a Twisted Application Plugin for twistd as per http://twistedmatrix.com/projects/core/documentation/howto/tap.html I want to distribute my app as a tarball, so the user would untar it and run "python setup.py install". Then they would run "twistd myapp" to start it. How do I configure setup.py so that twisted/plugins/myapp.py is created? Where do I create the twisted/plugins directory? (I see how this works if I run twistd from the directory containing twisted/plugins, or if I set PYTHONPATH, but I don't expect my users to have to do this). Cheers, Chris