The third thing that MC can add his BP to is spells or should I say special Spells. As these spells are mostly exclusive to our MC and no one else is shown to have these spells.
Equivalent Exchange: Uses 1 BP, First uses User's MP to damage the Opponent's HP, if that's not enough use it's HP until either the User or the Opponent dies.
Warp: Uses 1 BP, the User can travel to any location he has been to. The restrictions of Dungeon Walk as well as Field Walk doesn't apply to this Bonus Spell. But it still needs a flat vertical surface at both the place he goes from and the place he goes to.