X-Cart forums - Google Checkout & Conversion Tracking

I would like to track Google Checkout sales with a 3rd party tracking pixel. To do this, I need to add a tracking beacon using parameterized url's. The file to modify in x-cart is gcheckout.php; there is a solution for version 4.1 found here: http://forum.x-cart.com/showthread.php?t=40549 but this will not work in version 4.3.

Third-Party tracking info from Google is here: http://code.google.com/apis/checkout/developer/checkout_pixel_tracking.html

Has anyone been able to successfully add this?