BPAY for Accounts Payable

We are based in Australia and are looking to use BPAY as an alternative
method to paying a number of our vendors. We are looking for solutions for
where to store the Biller Code and CRN (customer reference number). The CRN can
change with each voucher received for a vendor in a similar way that the voucher/invoice
number. We would like to still use the invoice number for the voucher 'invoice number' and not use this
field to store the CRN. Using the bank account fields to store the biller code
and CRN would be OK if the CRN did not change, but where the CRN does change we