A few ideas come to mind:
Martial classes only, plus swordmage and paladin available via multiclass. Be stingy on the items with significant special effects, but generous with basic +n magic items, and things like flensing weapons or veteran's armor.
Light armor and small shields only, but change how the proficiencies work: instead of cloth/leather/hide/chain/scale/plate, use cloth/leather/hide/githweave/drowmesh/earthhide (the latter three from the Adventurer's Vault. This would mean that ACs would be a little lower, but there would be very few check penalties and no speed penalties for any armor. To compensate for the lower ACs, every military and superior melee weapon has the Defensive property, giving +1 to AC. If it already has the Defensive property RAW, then up the bonus it has to +2 AC. Allow rangers to wield two rapiers, as if they were versatile weapons.
Skill checks during combat never require a move action or a standard action, only a minor, free, or no action. Any skill check that would normally require a standard or move action becomes a minor action instead. This means that, yes, you can move your full movement, then make an Acrobatics or Athletics check to slide down a banister or leap onto a chandelier to get the drop on the enemy. In fact, allow any particularly clever use of a skill check in combat to add +2 to the player's attack roll for that turn. This goes for the obvious (Acrobatics, Athletics, Bluff), and the less obvious (Stealth to slip behind the tapestry when no one's watching, only to leap out and run one of the count's henchman through with your blade; History to recall that keeps from this era were notorious for their terribly-made floors, making it possible to stomp one end of the floorboard to send the other end up, unbalancing the guy on the other end).
Use an awful lot of minions, and a whole hell of a lot of skill challenges. Until the final momentous duel you have planned with an major enemy, the players should not be able to kill him/her. Depleting the foe's HP should, until the final confrontation, result in the enemy cursing the heroes' names, lineages, and meddling nature, all while beating a hasty retreat (that the PCs cannot fully stop, only complicate). I can't decide if critical hits or depletion of HP to zero should result in a major foe acquiring a scar/lasting injury from the attack, but there really must be some way to allow for that.
And here's an idea off the top of my head, that would obviously need some refinement: Divide the value in GP of all treasure parcels by 100, rounded as in math class instead of the "always round down" in the RAW. Instead of treasure, each party member gains that many "Romance Points" at the appropriate time in the adventure. Now, look at the values listed for each item in the RAW, and divide them by 100, and round them the same way--a level one item has a "cost" of four romance points, a level two item has five, etc. By investing a number of Romance Points in an NPC, the PCs can thus charm that NPC into falling in love with them, and giving them an item of cost corresponding to the number of Romance Points invested. "Oh, you dashing rake...! I could never allow my husband, the Duke, to have you killed! Here, let me unlock those chains--now, take this sword, and make your escape!"
The obvious question is "Why divide everything by 100? Why not just keep the costs as they are?", and the answer is that swashbucklers have no time to deal with three-digit numbers! There's adventure afoot, and villainy to thwart!
