In the pp_confirm.php you can make sure you are passing the SKU instead of the ID... so on lines 108-109 update:
$WA_PP_ECO_Do_itemized[0][$nextIndex] = "Number" . strval($cartIndex+1) . "";
$WA_PP_ECO_Do_itemized[1][$nextIndex] = "".$MotleyCart->DisplayInfo("ID") ."";
to:
$WA_PP_ECO_Do_itemized[0][$nextIndex] = "Number" . strval($cartIndex+1) . "";
$WA_PP_ECO_Do_itemized[1][$nextIndex] = "".$MotleyCart->DisplayInfo("SKU") ."";