PS: at the moment i can only come up with running the thing 2x by adding the following to your functions php

add_action( 'wppizza_on_order_executed', 'my_wppizza_google_cloudprint', 99);
function my_wppizza_google_cloudprint($orderid){
$wppizzaGCP=new WPPIZZA_GOOGLE_CLOUDPRINT();
$wppizzaGCP->wppizza_google_cloudprint_order($orderid);
return;
}

not tested, but will probably also slow down the last stage of actually submitting the order as it will be running 2x of course…

or perhaps just adding

add_action( 'wppizza_on_order_executed', 'wppizza_google_cloudprint_execute', 99);

might also work