How does it create more work? What do you mean switching between keyboard and mouse repeatedly? Aren't they already doing that when they are entering in the credit card number, the security code AND their name? LOL.
Doesn't matter, that's a "power user" shortcut. You'd be surprised how many people do not think or know that can be done. Why not make it easier and just make the expiration date text fields? It's much easier to type in the month '12' than having to scroll scroll through 11 options to get to 12.