You can’t use simples3 out of the box on Google App Engine because Google wants you to use their APIs for URL business. Ask them for the reason.
At any rate, there is support for this kind of thing too – all you need to do is be sure to use the right subclass, like so:
>>> from simples3.gae import AppEngineS3Bucket
>>> bucket = AppEngineS3Bucket(usual_arguments)
>>> bucket.business_as_usual()
And that’s it.