I haven't looked into it either, but you made me do it right now. Comment meta works just like post_meta. You can add this to your functions.php file:
// Add action to do after comment is submitted
add_action('comment_post','comment_ratings');
// After Comment is submitted
function comment_ratings($comment_id) {
global $wpdb, $user_identity, $user_ID;
$rate_userid = $user_ID;
$star1 = $_POST['comment_post_ID'];
$prevrating = $_POST['prev_rating'];
$totalrating = $_POST['total_rating'];
$totalrating = ($totalrating + 1);
$star2 = $_POST['star'];
// This is where the comment meta is added, just adds number to current comment meta
update_comment_meta($star1, 'rating', $star2);
// If no rating just insert it into the DB
if ($prevrating == 0){
update_post_meta($star1, 'rating', $star2);
update_post_meta($star1, 'total_rating', $totalrating);
// If it has been rated before Do some math and then insert it
} else {
$finalrating = ($prevrating + $star2);
update_post_meta($star1, 'rating', $finalrating);
update_post_meta($star1, 'total_rating', $totalrating);
}
Two things I have a hidden field of previous rating, so this doesn't have to do an extra mysql call here and I have the star rating form on the comments form.