I was reading through the T&C of the Southwest Credit cards when I stumbled across this:
This product is available to you if you do not have a current Southwest Rapid Rewards Credit Card and have not received a new Cardmember bonus for this card in the past 24 months. This does not apply to Business card and Employee Credit Card products.
I highly doubt it would work, but from the language, it seems as though you could apply and get the bonus from two different cards so long as you didn't have them both at the same time. Just wondering if the language has always been this way.