This is a great contribution and one I definitely want to use, but unfortunately I too am receiving:
Fatal error: Call to a member function pre_confirmation_check() on a non-object in /home/htdocs/includes/classes/onepage_checkout.php on line 548
I notice lines 547 and 548 (below) of onepage_checkout.php start with $GLOBALS. I'm a complete novice here, but does this error have anything to do with register globals being switched off?