How can I prevent Esther from blowing all her magic on songs?

It seems Esther will happily burn all her mana on party buffing songs that aren't really necessary on the first random bunny we find outside town. I'd prefer it if she would save her mana for boss fights and bounty hunts instead.
I know about the Tactics option for "Don't Use Abilities" but I still want her to use low-mana offensive familiar spells while I control Oliver for his more flexible spellbook. However, the expensive buff songs like Quick March and Cheer are built-in to her character, so I can't simply disable them by swapping familiars out. Swaine doesn't have a large mana pool for familiar special abilities.
How can I have the AI use Esther as an offensive familiar caster and not a coffee-addict bard?
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