Poland split payments - Supplier & VAT amounts

Poland has initiated a new requirement to split the supplier payments between the good/services to be paid to the supplier and the VAT amount to be paid to the government.

We send the electronic payments to the bank who then splits the payment as needed.  One of their requirements is to pay a single invoice within each payment.  Each payment has an instruction line to document the invoice number and VAT amount - only 1 invoice is allowed.

The question is this - how do the credit memos get processed when they are < 0 and don't get selected for payment when the Pay Alone Flag is set to Yes.