First download your data as described here.
Then install Charles Proxy App, start the proxy. Set in Proxy -> Proxy Settings to use not the 8888 port.
Finally start your development server and run this in the console.
$ python /path/to/library/google_appengine_python_1.5.5/appcfg.py upload_data –url=http://localhost:8888/remote_api –file=test.csv –application=your_app_id –email=you@gmail.com –passin
