Generally, NF men have plenty of masculine in them. Afterall, everyone has both masculine and feminine aspects. So I don't think the lack of masculine is the real problem here. Rather, it seems common that NF males become aware of their feminine sides at a younger age, during a time when adults and younger boys (and girls, sometimes) can be extremely cruel about behavior that doesn't fit a societal expectation of masculine. So we learn to resent the feminine aspects of ourselves.
Oddly enough, I think that this resentment of the feminine creates a situation akin to trying to not think about a pink elephant when you are told to not think about a pink elephant. It's the difference between trying to develop masculinity, and trying to not be feminine. So ironically, NF males will sometimes learn to hide their tendencies to be feminine with exaggerated expressions of femininity - such as trying to assert dominance by going into an emotional rage.
I think a big part of this is simply accepting how our feminine aspects affect our thoughts and feelings... so we can be aware of it and then choose to act on that or move beyond it. Beyond the emotions exists the empty void that guys spend their life dancing with, and in my opinion that emptiness is one of the sources of masculine energy.
There's another element to this whole thing that I think will especially resonate with most NF males, and that's the need for a Purpose in Life. This is actually where I'm stuck right now, so for the time being I got nothing on how to discover and integrate this. But I do believe that a lot of things fall in place once an NF male is directing his life towards fulfilling his Purpose, and perhaps that is one of the most powerful expressions of masculinity that we can offer the world.
And I'm quite sleepy, so hopefully that actually made sense.