dschep is dead for some reason, so copying & pasting his answer so all can see:

Duplicity[0] supports it through a boto[1] backend. [0] http://duplicity.nongnu.org [1] https://github.com/boto/boto

Depending on what functionality you need, one alternative could be Tarsnap (http://www.tarsnap.com/) by HN's own cperciva https://news.ycombinator.com/user?id=cperciva.