OK, i found the solution, here we go:

<?php

require_once('ripcord.php');

$url = "http://yourdomain.com";

$db = "yourdb";

$username = "youradminuser";

$password = "yourpw";

$po_id = 1;

$common = ripcord::client("$url/xmlrpc/2/common");

$uid = $common->authenticate($db, $username, $password, array());

$models = ripcord::client("$url/xmlrpc/2/object");

$models->exec_workflow(

$db, $uid, $password,

'purchase.order', 'bid_received',

$po_id

);

$models->exec_workflow(

$db, $uid, $password,

'purchase.order', 'purchase_confirm',

$po_id

);

?>