I wonder if your solution designer has taken into account some potential problems resulting from such item split.
If the customer orders a really big quantity of the same product (which can still fit onto a single truck), it could split into hundreds of items. Apart from the performance impact, you have a limitation for the number of items when posting documents to Finance, so you need to have a routine for splitting invoices. In some countries there is a rule - one delivery -> one invoice. This means that you may need to capture that earlier - during delivery creation and introduce delivery split at that time.
On top of that, having several deliveries for the same customer could result in planning them onto separate shipments (if the transportation planners are not very disciplined) and in a lower efficiency in terms of reducing transportation costs.
I can understand somehow splitting into separate lines between full and partial quantities for logistics purposes (if you have automated warehouse for full pallets and a smaller site nearby for manual picking activities), but I would expect just two lines in this case - one with 40 and another with 4.
Why do you need to have split per carton in the order?
Are you trying to communicate with some external warehouse system or this is for other purposes?
If it is for warehouse - is there no technical possibility just to send/receive pack proposals?
Not that it is impossible to implement such development, but is this really a good solution in your specific case?