I actually had to do all this

Code:
//    if (CURL_PROXY_REQUIRED == 'True') {

//      $proxy_tunnel_flag = (defined('CURL_PROXY_TUNNEL_FLAG') && strtoupper(CURL_PROXY_TUNNEL_FLAG) == 'FALSE') ? false : true;

//      curl_setopt ($ch, CURLOPT_HTTPPROXYTUNNEL, $proxy_tunnel_flag);

      curl_setopt ($ch, CURLOPT_PROXYTYPE, CURLPROXY_HTTP);

      curl_setopt ($ch, CURLOPT_PROXY,"http://proxy.shr.secureserver.net:3128");

//      curl_setopt ($ch, CURLOPT_PROXY, CURL_PROXY_SERVER_DETAILS);

//    }
I wasn't sure where to define CURL_PROXY_REQUIRED, so I just commented it out. For this server, good enough.