Master Morality IS Strong Will;by this very act of overcoming/surpassing/exceeding,one IS being a Master.

Nietzsche says;"ETERNAL LIVELINESS is what counts".['Human II,386]

You must desist from the musty belief in 'freewill',and think necessity through to its very end.To quote again from that very fertile book;
"THE FATALIST-You HAVE to believe in Fate - science can compel you to.What then grows out of this belief in your case-cowardice,resignation,or frankness and magnanimity-bears witness to the soil upon which that seedcorn has been scattered,but not,however,to the seedcorn itself-for out of this anything and everything can grow".[H,363]

Returning to the notion that overcoming IS this Master Ethic itself;"WILL A SELF-Active,successful natures act,not according to the dictum 'Know Thyself',but as if there hovered before them the commandment:WILL a Self,and Thou Shalt BECOME a Self.-Fate seems to have left the choice still up to them;whereas the inactive and contemplative cogitate on what they HAVE already chosen,on ONE occasion,when they entered into life".[ib.,366]