Check out this guy's webpage ( http://www.catspawcomics.com/sept/sept.html ). He has a lot of PDFs of material he's written up, and the combat one has rules on greatsword type specialization, including using it as a double weapon. It boils down to: take the Greatsword feat (prereq: str 13, BAB +1) and you can use the maneuvers from the combat PDF, including pommeling as a double weapon, clearing an area, etc. That's the moral equivalent of just using an exotic wpn proficiency on it. Without the exotic wpn prof, use it like a regular greatsword.
But you can read the PDFs, lots of good stuf there.
