1) In Website Settings, go to Domain Aliases and then add static.yourdomain.com. (replace yourdomain.com with your actual domain)
2) Once this is added, go to Custom DNS, and edit the root A record for static.yourdomain.com to point to 126.96.36.199. You can also set the TTL of this record down to 600 seconds if you wish (it means that it won't be cached for very long should the IP ever change).
3) After you have done this, you will need to log into your site and set it to use this domain for your static content. In WordPress for example, under Settings > Media, you would set the full URL path to http://static.yourdomain.com/wp-content/uploads nb: This needs to be the url to the actual uploads folder for wordpress. In Magento you would set the Unsecure Base URL for media. If you're not sure how to do this using your specific software, just get in touch for assistance.