De-couple Card number from Billing address

Hello,

It appears that the only options currently available to customers during the Checkout process is "Use existing card/billing address combo" and "Enter a new card number and its billing address."

To me, uc_cim should behave similar to the way Amazon's checkout process works: a user can enter a new card or select an existing one (by clicking the "Change" button), and they can use their default billing address for whatever card they select (or choose a different one / enter a new one). There's no real reason for these things to be tied together the way they are; a customer could change their address, and the only way to adjust this in uc_cim would be to go to user > edit > Manage Credit Cards > edit card, rather than just going to Checkout and selecting the two items independently.