Sébastien Fauvel commented on Apply Coupon Before Entering Billing Information

Our workaround at Darwin Pricing (see https://apps.shopify.com/darwin-pricing): Whenever we place a discount banner on a store, we add a tooltip to let people know that they should enter the code after checkout. The tooltip automatically pops up when our customers select the code to copy & paste it.

Here's our code snippet (the "title" attribute alone does the trick, the rest is just basic styling):

<div class="fc dynamicDiscount" title="Don't forget to enter your discount code after checkout!">
  10% OFF YOUR ORDER ! Discount Code: XYZ</div><style type="text/css">
.fc.dynamicDiscount {
  background-color: #96bf48; border: 1px solid #7a9d37; border-radius: 2px;
  color: #ffffff; text-shadow: 1px 1px 0 rgba(0,0,0,.3); font-size: 14px; font-weight: 300;
  line-height: 30px; padding: 0 9px; margin: 0 0 0 10px;
  text-align: center; vertical-align: middle; white-space: nowrap;
  display: inline-block;
}</style>

Hope it can help!