Just Add Extra Discount The Order Total

[hdeng]

I have searched quite a bit, but couldn't find a solution myself. Basically I want to be able to edit order, pretty much like ebay, at the total end, there is a discount / fee input field, you can add new entry (either discount or extra shipping fee etc). It's convenient for admin where he / she wants to give this customer extra discount or adjustment of shipping cost. I know Order Edit can do this, but you can not randomly add a new discount but update one already exists.