In order to install US only apps on your Xbox 360 you will need a US Xbox Live Account. Please follow the guide below.
- Go to http://www.xbox.com/en-US/live
- Click the sign up link
- Look for Don't have a Microsoft account? Sign up now and click the sign up link.
- Fill out the form and make sure to set USA as country - choose a US zip code like 90210
- Go on and upgrade to Xbox Live Gold
- When filling out the info make sure to use a fake US address. Use zip code 90210, Beverly Hills, California or something of that nature.
- Now you can login with your new Xbox Live Gold account on your Xbox and install US only apps.