My copy only says:
Armament Shield (Ex): When wielding a one handed weapon in two hands or a two-handed weapon, the weapon is treated as a light shield for the purposes of performing a shield bash attack on an opponent. The warder smashes with the butt of a spear-haft, the pommel of a greatsword, or the broadside of her axe. All are essentially the same and are treated as light shields for the purposes of shield bash attacks or martial maneuvers to be used with a weapon of this type (such as Iron Tortoise maneuvers that require a shield to function).
It makes sense to me that taking 2wf would work, but I wanted an absolute answer.