Do a lot of takes of the lead and comp and edit to perfection. De-ess manually ie gain change destructively in the audio file. Make sure that the vocal is pitch perfect ie better then real. Don't just slam an Auto tune (or similar) plug in across the vocal track. Either automate the plug or even better again manually fine tune every note that is slightly dodgy. Track Bv's 4 times ie 2 on the left 2 on the right including a lead double. So if we're talking pop music that'll be 1 harmony triad + double and a possible octave that would make 22 backing "vocals" takes. Use the cycle record and have the singer sing the part over and over. If you're also mixing check out interviews wiht guys like Dave Pensado and Tom Lord Alge. Hope this helps tho personally I'd play him some records from the 70ths and hope that he would come to his senses :)