How to automatically format multiple payment files in the same payment batch

Background:

We have a business requirement to process large batches of payments using a complex custom template. Initially when trying to pay 20k+ payments in one batch, the format payment files process ends with error read time out. We raised an SR to troubleshoot this with Oracle, but in the meantime, have been doing lots of POCs to determine if this is a performance issue. We later found that splitting the large payment batch into smaller chunks helps with the execution time and prevents the format payment file process from erroring out. However, we now are facing another issue where the