That's not the whole form handler. You have a misc class that it uses (included.) It has a custom method called send_email()...
/* starts at line 61 */
// Send Mail
$sent = $misc->send_email($_POST['name'], $_POST['email'], $emailaddress, $_POST['message'], $_POST['subject']);
You'll need to modify that method in the misc class or not use it in place of the mail function. However, since mail() is inherently insecure, you might just wanna add another parameter for bcc to the send_mail() method. The following is a very rough approximation of the misc class:
class misc {
//...
function send_email($name, $to, $friend, $message, $subject, $bcc="")
{
//...code is in here, you need to add to the header as instructed in my first post.
}
//...
}