Fish tape though vents

Hey I'm trying to get some Cat6 though the vents, any ideas on how to do it with fish tape/pole? I bought the tape already but I can't seem to get it to where I need it and I'm unfamiliar with ventilation systems.

Yes before you say it I'm aware of using plenum cables in the ducts and will definitely do so when I find a route.

Cutting drywall or drilling is unfortunately not an option.

I'm trying to get one from an upstairs bedroom to the mid floor and from the basement to the mid floor, any tips or info from you professionals would be greatly valued.

Also I hope this is the right area for this question, don't know where else to post it.

I have never had to do this, and it really is going to depend on the exact way that things are laid out, so without seeing it, it is hard to say. However, there has to be a way to get it done. You could try tying the fish line to an rc car and drive it through the vents or something.