Add ORDER NUMBER to the Subject Line of Emails

Please Add ORDER NUMBER to the Subject Line for all Emails, especially the Admin emails.
Or make this a CONFIGURATION item.

Many of my clients are using Google Apps (Gmail) as their mail client, which is a threaded email system.
Gmail GROUPS all emails together by the Subject line. Thus all administrator order emails get placed into ONE email thread. This makes having a conversation with a customer very difficult as multiple discussions with different people will all be together in one thread.

I have been using the hack to do this in administrator/component/com_hikashop/class/order.php but that gets wiped out each time there is a HikaShop update.

Thank you!