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, just like a 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