I'm really not sure how you use the code at the gas pump. I could mail you the $5 card instead if you like. I also know there is an option on the website where you can use one gift card code to pay for or refill another card. You may be able to do it that way.
Quick update... I sent my husband to the store to pick up the card and he chose a pretty colored one with colorful Easter eggs or jelly beans on it. It's kinda cute.