Instead of that, do something like say. . .Weapon Supremacy. Requires 18 Fighter. That's a feat in the PHB2.
Or perhaps Improved Two Weapon Defense and Greater Two Weapon Defense. If they can figure out the coding, perhaps the Improved Buckler Defense, and then allow equipping a two-handed weapon along with a buckler.
Bigger trick, and far cooler, could be the Tactical or Weapon Style feats from the Complete Warrior.
Trick to making Fighters more powerful is adding more and more feats.