Hi, I have around 2000 registered users in Joomla and want to add them to K2 so they can add comments - how can I automatically add them?

Just to add to this - is it possible to automatically add Joomla registered users to K2 if they edit their K2 profile? At present a registered Joomla user can edit the K2 profile and save but it still does not add them as a K2 user - if the "save" were to automatically add them as users, this would get around the issue of no sync of existing users between Joomla and K2 - any thoughts?
regards
Mike