Interestingly, half-swording (holding the blade with your other hand, as UngehuerLich suggested) would make an excellent alternate minor action for longsword or other versatile-weapon fighters. Quicker, easier to block with, and capable of devastating short-ranged strikes. Unfortunately, the primary downside of that is a loss of reach, and since in D&D a dagger and a flail have the same reach (!), that doesn't give us something we can use easily.
Perhaps a feat:
Half-Sword - Requires fighter, proficiency with a versatile weapon
While wielding a versatile weapon with two hands, you can use a minor action to switch to a half-sword stance until the end of the turn. While in this stance your AC and Reflex against melee attacks is increased by +1, and you inflict an additional +1[W] on any critical hit, but you still use the one-handed damage for your weapon and your melee and close attacks provoke opportunity attacks from your target(s).
Something like that.
Oh, and for anyone interested in more accurate depictions of Western armed martial arts: check out the tabletop RPG The Riddle of Steel by Driftwood Publishing (now out of print, but available used if you look for it) and the computer game Mount & Blade by Taleworlds. Both make heavy use of actual medieval texts on hand-to-hand combat and other strong realism elements. Very different from D&D, but very good.