Requiring a floor 50 clear with that particular job might be a middle-road suggestion to what you're wanting, or perhaps a SSS type instance (where your character is set to level 60) would work.

Putting dummies in Palace floors themselves brings up some issues:

1. Patrolling mobs. Most dummies are placed in secluded or safe-ish areas where you won't be distracted.
2. Trying to make use of the dummies within matched parties, as pointed out before. Unless the 2 others are willing to help or sit through it, this would likely just annoy them.
3. You're given 60 minutes to clear each set of floors. Eating up part of that with a rotation lesson isn't ideal.