There is currently no easy way to display past events in the widget that comes with the plugin. I’m afraid it would take some custom development that would be beyond what we could do here in the forums.
That said, this is a feature we’ve seen come up on our UserVoice page, though it looks like that ideas was declined. Also, here’s a direct link to our Themer’s Guide and our documentation to help get your started with possible customizations.
Sorry I don’t have a concrete solution for you here, but does this at least help answer your question? Please let me know.
Thanks,
Geoff