Nginx Load Balancing

I want to load balance my website with nginx.

The load balancing in nginx wiki is proxy, so the actual file being downloaded from the frontend server. (http://wiki.nginx.org/LoadBalanceExample)

This is how I need the balancing:

user request file:

• http:// site.com/image1.jpg

nginx redirect user to one of the servers (with Location header):

• http:// s1.site.com/image1.jpg
• http:// s1.site.com/image1.jpg
• http:// s3.site.com/image1.jpg

Is this possible with nginx?

http {
  split_clients "${remote_addr}" $server_id {
    33.3% 1;
    33.3% 2;
    33.4% 3;
  }

  server {
    location ~* \.(gif|jpg|jpeg)$ {
      return 301 "${scheme}://s${server_id}.site.com${request_uri}";
    }
  }