Bit of reviving an old thread but I was just dealing with something similar and thought this might help others. I wanted a click track in my headphones but not on any output elsewhere.
What I ended up doing was making a separate audio track, inputting the metronome to it and then looping it for the length of the song (after recording one bar). Then I just set the output on the audio metronome track to my headphones and lock that audio track.
From there you can delete the instrument metronome track and automate the audio metronome track from a control track if you want to turn it off after two bars.
It’s a marginally annoying way of doing it. But effective and beats my first thought of making a metronome track in another daw and importing it.