How to generate bill by OR payment method on multi stop shipment

Our client gnerates multi stop sell side shipments to maximise revenue from the customer from rate breaks. However they wish to use different payment methods on some OR and as a result want to generate different bills for each payment method.

Is there any way to automatically generate different bills from the same shipment by payment method.

Alternatively is there a way of splitting the bill by OR to achieve the same result?

Thanks