Matty, do you think I have to worry about the mini-plugin you suggested no longer working after future upgrades (or recent upgrades)?
function s2_remove_subscriber_role($subscribers) {
$user_query = new WP_User_Query( array( 'role' => 'subscriber', 'fields' => array('user_email') ) );
$subscriber_role = $user_query->get_results();
$exclude = array();
foreach ($subscriber_role as $user) {
$exclude[] = $user->user_email;
}
return array_diff($subscribers, $exclude);
}
add_filter('s2_registered_subscribers', 's2_remove_subscriber_role');