Subtler display of coupon discount fields

We provide some registrants with discount codes, and need a way for them to enter these when registering, so I enabled coupons. However, the design of the registration form is not ideal, because it really emphasizes to all users (including those who do not have a discount code) the calculation of the discount:



For users without a discount, this unnecessarily gives them the feeling they are missing out. Instead, it would be nice to have a discreet box, or hyperlink, to add a coupon code, and only then start displaying the other fields (Discount Amount, Gross Amount). For example, here's how it's displayed in Virtuemart (the system we're migrating away from):