Most bands I record (including my own) have singers who do this.
If the parts are DEFINED (like nothing inbetween...clearly there are singing parts, and screaming parts), then I say record it seperately. get the right levels for each, put em on seperate tracks. usually i compress screaming a bit more than normal vox - to really bring out the gut of the screams.
if it is really spiratic and random, I just set the level low enough for the loudest parts (screams usually..ha)...then let the vocalist do his thing. Then, when i mix - i try to cut up the parts, so anything that is clearly singing, I can just copy to another track, and leave anything that is screaming or close to it on a track. then, i still have the ability to mix/compress it differently if needed.
you just gotta be careful though
oh yeah, and I'm using a computer - so i have that ability easily...with 4 tracks you may not be so lucky.