You need a 3rd party provider (in the US). You connect to that provider, setting up a VPN tunnel between your computer and their, and then pass your traffic through it. To Amazon it then looks like your traffic is coming from the providers machine (in the US) instead of from Mexico. A VPN service might not be foolproof though - depending on how paranoid Amazon is, they might block IP's from known VPN providers, just like they block foreign ones...

I'm not up to date on US VPN providers, but a good start I'd assume would be to google 'US VPN' - but I'm sure others here will have recommendations.

Swedish VPN services tend to be about 50SEK (~US$ 7.00) / month.