If he puts minoxidil on his penis, it might dialate those blood vessels more than the rest. But it would then get in his woman, and make his penis hairy, and might damage those blood vessels. Might not go deep enough either, or the increased circulation could take it systemic fast. If all blood vessels dialate at the same rate, the penis would not be bigger.
Minoxidil does not have hormones in it. Putting it on your head will not affect your penis. And putting it on your penis sounds dumb for the reasons mentioned above. And I think alcohol on your penis would burn.