Option to split delivery costs across multiple PO’s

We place multiple PO’s to our supplier which then very often get combined into a single shipment for cost saving & efficiency purposes. 
The entire shipping cost is then invoiced either on a separate invoice or sometimes all combined and added onto one of the PO’s. 
This then leads to inaccurate landed costs. 
A feature to split “additional costs” from one PO/invoice across multiple PO’s would significantly improve the accuracy of landed costs.