Ever noticed, or played Name That Tune? I could do it in one or two notes with 80% success. Same with signing along, I may not have heard the song in years and couldn't sit and write the words down, because I couldn't remember them,,, But if I sang along with the song I could nail it word for word, on pitch, hit the Steven Perry , pitch perfect, Don Henley, Vince Gill, Ronnie James Dio, even Ann Wilson.,,,, I always knew I was feeding off them, Same back in school singing in choir,,, other's would feed off of me and if I stop singing others would follow suit or get all screwed up until I came back in, and all would be fine, so what I'm getting at is use a fine pre-delay between that vocal, to monitor/phones, record that, then use that with the better part of the whole composition, (as a feeding source for the vocalist) and do another vocal track off that. If this doesn't make since, then put on your favorite song, sing along you'll think S#*T,,, I sound pretty damn good

Then hit the mute button.....and you'll get that WTF feeling. Case Closed.