whmcsTools/orderdetails.php

<?php
if (!defined("WHMCS"))
    die("This file cannot be accessed directly");

add_hook("EmailPreSend", 1, function($vars) {
	if($vars['messagename'] == 'Order Confirmation') {
		$result = localapi('GetOrderDetails', array('orderid' => $vars['mergefields']['order_id']));
		return $result;
	}
	return false;	
});