Automatically apply promotion codes before checkout

I understand that the current functionality is the same used on many other online sites. However, I believe it would be a huge boon to our customers if Pressero would automatically apply any entered promotion code before order submission.

We have far too many customers who do not read the instructions and fail to click the apply button next to the promotion code input box. Then they are unable to apply the code to the order because that can't be done to a pending order (that's a different issue).