I might be missing something here but if you send them a payment they will post it to your account regardless if you have a balance. If the purchase is still pending then you'll have a credit toward that purchase posting. I don't see the problem.
Because the chicks dig it when I throw down the card to the waiter and...it comes in handy if I'm short on cash until payday and need a short spot. AMEX gets the booty, and that's important when you're a Pirate.