Is there a class or set of feats that focuses on shooting with the ballista?

I’ve tried to do a little research, as my players will soon fight pirates, whose warship is armed with ballistas (gunpowder hasn’t been invented yet). Unfortunately, I was unable to find any class that would exactly fit the role of a ballista operator.

Is there a class that gets bonuses for attack, damage or some other useful features for ballistae? The pirates should be around 12th–14th level.

I use ballista rules from Heroes of The Battle, both heavy and light.

If there are some useful feats for that, please do not hestitate to mention it. As far as I have found I have:

  • ballista proficiency
  • crossbow sniper
  • plunging shot
  • ranged weapon mastery

Materials from 3.0, 3.5, Dragon Magazine and Dungeon Adventures are allowed.

Just to clarify, as the gamemaster, I do define ballista as an oversized variation of crossbow, thus most of feats, classes or features that affect crossbows will affect ballistae as well.