Cards with additional costs that are mana payments don't require them when cast without paying their base cost

i.e. if you cast Daring Buccaneer or Flamekin Bladewhirl through a card that casts without paying mana cost (Electrodominance, Baral's Expertise), you won't be asked to reveal any cards or pay any extra mana. You should be, though, because these are *additional* costs, and they are not covered.

Other additional costs seem to work fine; it's just the reveal/mana ones that get ignored.