Accounting Reference field

In the absence of an accounting reference field on the SU we using the PO Number field to record this information.. We now have a SU that is being funded and their invoice requires a reference and I am told the PO Number field is where this should go when using a "funder" for payments.

So either we need an "Accounting Reference" field for and internal reference which would free up the PO Number to be using with bulk funders for the SU's or a "Funder Reference"  field needs to be added for the funder references..