The Netbook of Feats (a wonderful resource) contains the following:
BODY COMBAT [General, Melee]
COPYRIGHT 2001, Carl Cramér
You may add an unarmed attack to your attack routine.
Prerequisite: Improved Unarmed Strike, dexterity 15+.
Benefit: You gain the use of the Two-Weapon Fighting and Ambidexterity feats, but only when your off-hand weapon is an unarmed attack such as a kick, knee, elbow smash or head butt or an armored variant of an unarmed attack such as a gauntlet, steel boot, kneepad, elbow guard or helmet.
Special: You can learn later feats for which Ambidexterity or Two-Weapon fighting are prerequisites based on the virtual’ feats learned with Body Combat, but you can then only use those feats when you fulfill the limitations of Body Combat.
Notes: Unarmed attacks are of a size code two less that the user, and so are always light weapons. With this feat, an armored boot, kneepad, elbow guard, helmeted head or similar object works like a gauntlet, with or without spikes, and they can all be used with this feat if you are proficient with them.
Will this do for your character, do you think?
As a side note, I actually saw a program on the History Channel that dealt with the style of combat you wish to portray. A manuscript exists that contains illuminated pictures that diagram attack and defense positions for a two-handed sword style of fighting. A British expert extrapolated from the illustrations to determine how each move would connect with the others. The result was a fluid style in which each attack routine put the swordsmen in an excellent defensive position at the end of a blow, poised for the next attack. The form relied as much if not more on balance and momentum as strength for its efficacy; the swordsman would move around his weapon as much as moving it around himself.
This wasn't the stereotypical 'stand back far enough to get a really good swing while holding your greatsword in a two-fisted grip' kind of fighting. In the course of his routine, the swordsman would shift his grip from one-handed to two-, and from the hilt to length of the blade. He would step in close, and wield his sword like a stabbing spear, club with the handle while grasping the weapon by the blade, bash with the pommel, or strike with the flat of the blade as if it were a quarterstaff. Mixed in with his weapon routine would be opportunistic unarmed attacks: elbows, shoulders, kicks to the legs, knees, and lower body.
Furthermore, the style took defense into account as much as offense. By staying in close to his foeman, the attacker would keep his opponent off-balance, and give him little opportunity to ready his own strikes. The swordsman's more powerful attacks would always result in his blade interposed between himself and his opponent, either in a guard position to deflect attacks, or with a sweeping motion which would force his adversary to back off.
Anyway, I thought it was interesting to discover that, historically, the two-handed sword wasn't just a dressed-up crowbar.