Add Bccs To Order Notifications

I'm trying to create a simple addon for adding BCCs to all notifications sent by the cart.

I'm trying to hook this onto the mailer_send_pre hook using the following function.

function fn_bcc_emails_mailer_send_pre(&$this, &$transport, &$message, &$area, &$lang_code){

So far nothing has came through when triggering the function. Does anyone have any suggestions on what I'd need to do to correct this?