On line 378 you could add:
if (sizeof($ShippingOptions)==0) {
$ShippingOptions["04"] = array("International","9.00");
$_SESSION['shipChoice'] = "04";
} else if ($_SESSION['shipChoice'] == "04") {
$_SESSION['shipChoice'] = "03";
}
Then add code to the confirm_cart.php so that it doesn't bother to try to recalculate shipping for international (line 54).
I've gone ahead and made those updates.