Add these hidden form elements to the hidden form at around line 464:
<input type="hidden" name="handling_cart" value="<?php echo($loon2->GetShipping()); ?>" />
<input type="hidden" name="tax_cart" value="<?php echo($loon2->GetTax()); ?>" />
<input type="hidden" name="bn" value="WebAssist.eCartPHP.Pro" />
(please leave the last one too... it won't effect functionality, but helps us get credit for the customer when PayPal evaluates our partner relationship)