Manually apply to invoices credit memos created outside Fusion and not applied during integration

We have several payable solutions that integrate to Fusion ERP, including credit memos. We would like to apply these credit memos directly to a specific open invoice. We are not creating the credit memos in Fusion. We are not applying the credit memos in the payable solutions and there are no reference to apply during integration. We have tried to apply the credit memos to a specific open invoice in the past without any success. Is there a way to apply the credit memos to a specific invoice in Fusion aside from paying together an Invoice and a