Triggering PO 7.4 interface based on a trigger file

I have a requirement in such a way that many files of .csv format are placed in an FTP Server. Once all the files are placed completely, a trigger file is placed of .txt format which intimates that the files are ready to be processed. As this is not scheduled on a daily basis, PO Interface has to be triggered based on the trigger file.

tried working through the below link.

The solution did not work as "Additional file(s)" check box is not available in PO 7.4.

Below images from SAP PO 7.4 and SAP 7.31.

can anyone please help me out and give a solution.