You can do this in the custom HTML section... wrap it in <script></script>
An HTML widget might also work.
I can only seem to use the default Gravatar thing and it doesn't allow you to change. Is this intended?
You have to change it at https://en.gravatar.com/
You can also upload from file or from external link, but currently there's a bug on the latest dev version on this community that prevents you from uploading (it should work just fine on stable 0.6x)
Heh, yeah apparently I figured it out!