Wouldn't it be easier to just bind the server to localhost? That way, the server should only listen on the loopback interface and not any of the external network interfaces. At around line 1974 of pydoc.py (Python 2.4.3)...

            host = (sys.platform == 'mac') and '127.0.0.1' or 'localhost'
            self.address = ('', port)
            self.url = 'http://%s:%d/' % (host, port)

Replace the '' with host in self.address by default, perhaps. Then, add a host parameter to the serve function and let this be used to override the above. Expose the parameter as a command line argument. I'll come up with a patch for this at some point, I suppose.