Not if they're guarding a sieze location.
The easiest way is to use an uber unit like Ike, put him within the boss' range, unequip their weapon, and let the boss hit him. Move him away next turn and have a healer heal him.
For your non-healer units, just give them a bronze weapon or two (since they can't critical), let the boss attack them during his turn, and let them regenerate to full health, and repeat the process.
It's tedious, but the Battle Save feature makes it far more beneficial than Battle XP.