No. Singing one line does not amount to a 'shared lead vocal' any more than it does in On The Border. A shared lead vocal is a song like King Of Hollywood or What Do I Do With My Heart.
I'm afraid the song is one of my least favourites & when I finally got to see it in 2015 I remained underwhelmed by it. It's a shame to say that now, I suppose, but it's the truth.