Communicating application of credits to suppliers

Often we will receive credit notes from suppliers for things unrelated to specific invoices, for example stock returns. At present we will apply these against whatever invoices are due for a given week until the credit is fully applied and there is still an outstanding invoice balance to pay.

Our current system puts anything that happens on the purchase ledger on the remittance the next time a payment is made. I have so far been able to build a custom print format that will show the invoices paid and any credits taken against those invoices, however I can’t see a way to show also any invoices that were covered in full by a credit (in the period between this payment and the previous payment to that supplier).

Does anyone know of a way to do this? We don’t want suppliers to be allocating credits on their own and we can’t manually tell them every time we apply a credit.