I used to use a bench grinder. Grind it down and keep checking. You'll see it pinkish before get to the blood. Think I drew blood a handful of times, but only a pinpricks worth.
If he gets to causing harm, it's useful to know hens are sperm storers. To lay fertile eggs they don't have to mate before each egg is laid, one mating results in fertile eggs for something like 14 days (don't remember exactly). So if you have another run/house, you can shut your boy off hens apart from couple of days a week or so and still hatch out all the eggs.