Setting Marketo Program Event Partner via REST API?

Has anyone succeeded with setting the Event Partner in a Marketo Program via REST API? Our team is experimenting with connecting a live event in GoToWebinar with a Marketo Program (idea is to clone both, then set Event Partner all using API calls).  We haven't found any documentation from Marketo or GoToWebinar that makes us believe this may be possible but thought we'd ask the community in case there is a hacky solution someone has discovered. Thanks!