There is no way to add a feature like this on Octave, right?
https://www.mathworks.com/help/audio/ug/parametric-equalizer-design.html
looking at the examples on that page, and many of the functions they call (object oriented design tools like fdesign) are still listed as unimplemented in the Signal package, it likely is not currently possible to do exactly what they do. depending on your exact needs, there may be other ways to accomplish the tasks you need to do. Here are links to the current signal package with function reference, and the wiki 'missing' list: