How to transfer report files in csv format via ESS job to SFTP SERVER.

We need to transfer a report output as a single file to the SFTP server using an ESS JOB, so we're using a bursting query to specify the server name, path, and location. The bursting query requires a key column, so we've added a dummy column, resulting in a single output file. However, we need the output in CSV format, and in CSV, all columns from the data model, including the dummy column, are included. How can I send the report output as a single CSV file to the SFTP server without including the dummy column?