Some of us don't bother to finish off the cockerels before culling. I used to have a separate pen for cockerels but it's being used for a separate line of breeders now. I did several months of small, staggered hatches. Been culling the problem cockerels two or three at a time, every 10 days or so. Just separate them out the night before so I don't have to waste time trying to catch them in the morning. No special feeding plan. They taste great and the pen of youngsters is relatively calm. Works for me.
There is going to come a time not too far off when we just plain old can't shovel it into barrels any more! Bucked hay for winter sheep feed for the first time in years and it about killed us........