I'm sure there is a way to do what you want to and hopefully someone chimes in. I'm sure they will.

In any DAW, I typically copy the track that I want to use to make the harmony from then simply turn down the main vocal in that track coming from the effect. You simply delete any areas in the track you don't want harmonies then.

Another advantage to this approach is you could sing a new track only where you want harmonies and extend some longer or shorten the phrasing in other areas. That way not all of your harmonies are not always sounding like they exactly follow the lead all of the time. As an example, if you were going to sing the word "time" as part of the melody track and have additional lyrics after that word, you could sing the word as "tiiiiiiiiiiiiiiime" held out for your backing vox.

Just some ideas. Best of luck. I'm excited to hear your results!

Chad (Hope that makes it easier)

TEMPO TANTRUM: What a lead singer has when they can't stay in time.