How to create separate dunning letters per customer invoice stages

Summary:

In Fusion Collections we need to be able to generate dunning letters per customer invoice stages and not only one letter per customer.

Content (please ensure you mask any confidential information):

Currently, in eBS R12 we have a parameter 'Single Staged Letter' available for the concurrent program:
'IEX: Send Dunnings for Delinquent Customers' and by this we can control the letter delivery per customer or per stages. 

But for Fusion the official Oracle statement is as below:
"A single consolidated letter CAN be sent to eliminate sending multiple staged dunning letters to the same customer who has more than one delinquent transaction."