It looks like you have already found the "Frequency Response of Passive Circuit" demo model included with PLECS 4.4. Did you open the included simulation script? You can access it from the Simulation + Simulation Scripts menu.
The key command here is:
plecs('analyze', 'AC Sweep', simStruct); % start AC Sweep analysis
where 'AC Sweep' refers to the Description field of the preconfigured Analysis Tool. The scope data is read from a script.
Another good reference to refer to is the "Simulation Scripts in PLECS Standalone" section of the user manual. The "Starting an Analysis" section of the help describes an alternative to reading the scope data, where the transfer function is returned directly as an array.