If you want the best sounding vocal, you need to fix it before its recorded.
Try teaching the guy some proper mic technique. Move in comparison to the mic, depending on his volume.
As was mentioned before, record each part individually.
Also, what are you doing while he's singing? You should be watching your levels. Ride your faders and adjust as you go. That's essentially what compression is (In a very very general sense).
The less things you have to add to your signal chain the better. Fix it on the way it. Don't just sit and twiddle your thumbs while people are performing.
