Detail type data outputted across rather than down

I have a requirement for a csv file to be created that will be uploaded to a bank. The data is tied to a check run listing out the check number, vendor, amount, and invoices paid.  The pain is that the format is one row per check, and the invoices paid by the check are listed out recursively across on the same row, be it just 1 invoice being paid or 20 by that check. It repeats the invoice/ref number and amount paid (against the invoice) columns on the row.  Right now, the spreadsheet is maintained manually by the customer so they handle the uncertainty of how many invoices are being paid, column headings, etc..  I know the unknown of how many invoices are being paid is a problem.  I have a GI that lists what I want with each invoice paid being a new row, but no idea if that invoice detail can be placed going across rather than down.  I’m thinking it probably isn’t possible within a GI, but just wondering  if anyone has encountered this type of format/layout requirement and what any options are.  Thanks!!!