Tal vez puedas hacerlo así
Código PHP:
$host = "your.host.com";
$port = 80;
$postdata = "field1=value1&field2=value2&field3=value3";
if ($sp = fsockopen($host,$port)) {
fputs($sp,"POST /path/to/somescript/php HTTP/1.0\n");
fputs($sp,"Host: $host\n");
fputs($sp,"Content-type: application/x-www-form-urlencoded\n");
fputs($sp,"Content-length: ".strlen($postdata)."\n");
fputs($sp,"Connection: close\n\n");
fputs($sp,$postdata);
fclose($sp);
}