How to record a payment when voucher is a paid credit invoice

When we receive a credit invoice and there is no debet voucher available from the vendor sometimes the vendor pays us the credit amount. It is not possible to process the invoice via the paycycle. Also you cannot record the payment manually since the amount < 0.

To pay the credit invoice we create a "dummy" debit invoice to clear it. This is not a nice solution.

Does anybody know an other way to do this? We also have Financial Gateway where we receive bank statements. At the moment we also cannot clear the receipt in FG against the credit invoice...