Sadly you can only purchase Minecraft via a Credit Card or PayPal, or you can have someone else give you a gift code (best bet would be a friend who wouldn't mind to use their card). The only times I give out gift codes is if I actually want to GIVE someone the game.
... Don't look at me like that! Don't expect a free gift code from me!
You'll either have to make a PayPal account and use that, use a credit/debit card, or look for a friend that has either of the options handy (that you've known for more than a forum post). Godspeed!
P.S. Some stores can provide you with a Credit Card-like plastic that you pump your cash in. It is like a debit card using your checking account, but instead you just go to a store and put cash in it. This is so you never go "Over the Limit" and you can make purchases online with ease. Very handy for people who don't like to use actual credit cards.
Seeing how right now it is really just a "permission" thing I don't see how it would be possible via Amazon. Everything is digital. Heck, you can even download Minecraft right now (just can't log in without the purchase). Unless it is distributed by other means or supported by different third-party companies I wouldn't think so.
Shorter Version: Not right now, and nothing in the near future.