First and foremost, if you're going to do this, do it at YOUR OWN RISK. Understand that I accept no responsibility to any problem that you might face regarding this matter. I'm merely sharing the information on the 'workaround' for the non-US residents restriction on most if not all of the Digital Download titles on Amazon.
Obviously, this only works with DIGITAL DOWNLOADS. So make sure before you proceed with payment, u picked the correct category. You will still need a credit/debit visa/mastercard, and as far as i know, this is the only mode of payment that a non-US residents can use for the workaround and Amazon still doesn't accept Paypal.
All you need to do is just login to your Amazon account and proceed to 'Add a Credit or Debit Card' under the 'Payment Methods' sub-category. Enter your card number/details as it is but put in an US address! Best to use addresses from Alaska (google/map search for hotels) to avoid any tax issue. Once this is done, you can proceed with your purchase.
It goes without saying that this violated Amazon's T&C for digital games purchase and you're NOT eligible for support, troubleshoot, refund etc etc. So make sure you don't make mistake such as paying for the wrong product - double check on that 'PC/MAC DOWNLOAD' version! (probably works with PS3 Digital Code too)