Queu existing users for required lists

I seem to remember that in the 6.x-1.x branch, there was a way to send all of your existing users to Mailchimp during a cron run (assuming it was a required list). Is there any way to do this in the current 7.x-2.x branch?

Currently, newly added or updated users are sent to Mailchimp without a hitch... but what about existing users who are not yet in the Mailchimp system but who should be on a required list?

--Ben