If you have a kindle change your zone in the kindle settings page and add an US adress (pick one on the yellow pages). I am in france and use that method to download us only kindle ebook. It's work perfectly :) (amazon dont verify the postal adress)
But they may just ask you re-enter CC info OR validate it against your address as well.
Fun story: been living in the UK for a while, but using Lithuanian credit card to shop online. Most websites required UK billing address. And allowed to use my cc with billing address in different country...