What if you did the following:
Start with, say, Fighter:
Bump skill points to 4 per level
Add new skills -- say, the people-relating skills (Diplomacy, Bluff, Sense Motive, Intimidate, Gather Information) along with some Dex-based skills, but NOT Tumble. Swashbucklers leap, keep their balance, climb, and wriggle out of ropes, but they don't generally do backflips or cartwheels.
Lose many of the weapon proficiencies (give them Simple, plus any piercing martial weapon, plus any swordlike slashing weapon of medium size or smaller -- no axes, no claymores, no hammers)
Lose Heavy and Medium armor
Gain defense stuff to compensate for lack of armor -- like Cha-bonus to AC and a monk-ish Defense progression
Change save to Reflex good
Restrict the fighter bonus feats, or swap out bonus feats for abilities like the stuff I mentioned in my first post.
Everything else, you can flavor-up.