Thanks for the tip. He is a big boy. I'll probably just build another coop and separate the flock. For now, the bullied one get let out to free range with 1-3 hens.For an injured/traumatized bird like that I would use the broostick method (cervical dislocation). Quick and it shouldn't traumatize them.
For a rooster I would decapitate or cut the jugular like you would for butchering unless you are really strong since I've found that they generally have a thicker neck - maybe it's just me.