Reference Number in Copy Control VTFL

Dear Experts,

I have a scenario that two sales orders created with two different P.O numbers and created one delivery document combined these two SOs.

Now while creating invoice, system splitting the invoice into two as the PO numbers are different.

Here in copy control VTFL, reference number is given as A ( PO number) as FI wants PO number to be copied in acc. document.

Now how to handle this requirement using any routing/exits, so that system can pass the two PO numbers to Financial accounting document for reference.

Hope I have made myself clear.

Thanks,

Jagan.