Nominal fee? Nah, I give this info away free of charge! Here is my three step program to not breaking your knuckles.
First off, choose your weapon. Not all knuckles are created equally, use the large knuckles at the base of your fingers, not the knuckles of the middle joints of your fingers. Further, I personally reccomend focusing the blow on the knuckles of the middle and index finger. Dempsey can say what he wants, whoever would like to can agree with him, I don't.
Second, don't just throw your punch out there without any consideration for method. When you're in gaurd let your fist relax, not open, just relax. When you throw your punch clench the muscles of the fist and forearm, this will reinforce the wrist, it will also add speed and penetrating power. Don't lock out your elbow. I prefer a vertical fist, but horizontal works too.
Third, hone your weapon. Buy a child-sized heavy bag, not one of those 70lbs affairs. Hang your bag so it can swing freely a good distance in any direction. Set it in motion and practice slipping the bag as it approaches you and striking the bag as it swings away from you. Do this without gloves. If you want to do this hardcore like the old dads did, after such a session dip your hands in strong brine, weak tannic acid, walnut juice or similar. This will build bone density and toughen the skin, as well as other soft tissues. After you've been practicing a while you can try crushing large potatoes for fun. If you're hygenic about it you could even boil and eat the resulting product... I wouldn't.
For what it's worth, I've been in a great many streetfights in my day. I have never in all that time and all those encounters ever broken a knuckle, sprained a wrist, or anything of the sort.
Tomorrow's exciting event, dispelling the myth of loss of fine motor skills being an inherent reality of fighting... bwahahaha!!!
Till then, fair thee well and keep in mind that just because something is tactical don't make it true.