Using an INI file is not protecting your passwords. It's just obfuscating them.
You can implement your own obfuscation and read just credentials from some configuration file of your own, instead of using whole WinSCP INI file (It may cause you lot of troubles). Even better you can protect your configuration file with Windows file-level encryption and make it accessible with restricted account only (you can do the same with INI file obviously, or even easier, do it with your present scripts).
Anyway, to answer your question. I actually do not know what you are asking for. The
is a string property. Just set it with path to the INI file you have created with GUI.