S3Boto URL generation doesn't include Response Headers
backends.s3boto.S3BotoStorage currently generates a URL like this:
return self.connection.generate_url(self.querystring_expire, method='GET', bucket=self.bucket.name, key=self._encode_name(name), query_auth=self.querystring_auth, force_http=not self.secure_urls)
S3Connection.generate_url also takes a keyword argument "response_headers" as a dictionary that can determine the headers S3's response to the link.
See this link for more info: http://docs.amazonwebservices.com/AmazonS3/latest/API/RESTObjectGET.html
This feature is relatively trivial to add. Simply include a setting called AWS_RESPONSE_HEADERS to the s3boto module, and add the following argument to the url method on line 259:
I may add it myself at some point if I can bank on getting a pull request answered.