Personally, I think it will be something where in Gaban will tell Sanji that a conqueror that is divided is no conqueror at all, embrace who you are wholly? Basically telling Sanji that he needs to embrace his Germa side as a part of who he is fully. (I think would be cliche, but this is Oda so it could just be that simple)
Or something which i like better would be, Gaban tells Sanji that he does not have a conquering spirit but that which lurks within you does. Basically telling him that his alter ego is the conqueror.
Sanji: Hey Old Man, what about me?!
Gaban: Black Leg Sanji, I've heard of your exploits, though strong you may be, the will to dominate to enforce your will to make others bow, you do not possess.
Sanji:- (Dejected) No, so moss is... I don't have it
Gaban:- However, there resides another in you, one who has the will to subjugate who you must cede control to, only then will the conquering king reveal himself.
Sanji: Hey, what do you mean there's another me?
Gaban:- Exactly, what I meant - your other half Black Leg, the one who you have struggled to keep suppressed, the one whose visage terrifies you, the one whom you are afraid to give control to, the one whom you must release from the shackles of your insecurity.
Sanji:- H-h-hey, you dont mean that that Vinsmoke guy!
Gaban: A house divided against itself will fall, young man! Unless you can conquer your heart, how can you conquer the will of others.
Sanji:- How can I be sure he won't...I won't lose control?
Gaban:- Whilst you may not have a heart to conquer others, you Black Leg have the power to conquer yourself.
Sanji:- How?!
Gaban:- The Power of Love is a funny thing - though it can never be used to subjugate others, it can be used to dominate one's self. If you stay true to who you are, even the darkest depths of evil will cover at the blinding light of love.