Add support for groups in Mailchimp app

I have a specific client use case at the moment as to why this would be useful.

My client has a master Mailchimp mailing list that he uses to send regular updates to interested parties. He runs conferences, and invites people to sign up to receive updates to that specific conference, as well as being added to the overall mailing list. This is achieved by creating a Mailchimp group for that conference in that mailing list and adding them to it.

By default however, Mailchimp won't allow them simply to drop their email into a sign-up box if they're already signed up - they bounce them telling them that they're already subscribed. It won't handle it smartly - ie. if they're not yet signed up, add them to the list and the group, but if they are signed up then simply add them to the group. So I need to handle that logic at the site.

Obviously the easiest way for me to do that would be if the Mailchimp app supported groups, since it would save me delving into the mysteries of Mailchimp API myself!

I would have thought there would be a number of other mainstream use cases for this - Mailchimp have added groups because it is an often needed feature to be able to segment lists in this way.