Generating Column Header using FTP Adapter

I want to add a single column header in my CSV file being produced by FTP adapter in OIC. I understand we have to create a repeat node in the OIC mapper to add a header. But, my problem is the for each loop is outside the xslt as I have to populate different columns from different rest calls. Hence, when I am appending to the file each for loop creates a new header resulting in multiple headers in the file. Anybody can suggest how to get a resolution of this situation?