Yes you can use a fake US address and set your Kindle country to the US, but Amazon monitors the IPs (and credit cards) you are buying from and after a few purchaes to your fake US address, they'll start sending you letters asking for proof you live there and eventually lock you out (force you to change back to your real country) if you can't provide them.
Amazon killed a coworker's Kindle Fire account, because he was forced to add a test credit card - you can't use Kindle Fire without an U.S. cc, which sucks.
using a proxy/vpn and buying yourself gift cards from another account should give you reasonable protection, yes. As long as you have enough gift card balance, Amazon won't ask you to add a Credit Card. But it's cumbersome, etc.
Amazon recently started blocking my Kindle purchases basing on the fact my IP locates me in Japan while my primary address is set to the USA. When I switched to the gift option (using the same account) it worked without any problem even though I was still using the same Polish credit card.
