I'll eventually compile a full list, but a number of commands do seem to work, and yet not work..
Hopefully, I'll update it with complete info, but here's what I've found out.
Fight - Uses the Deathbringer/Black Sword animation
Dark Wave - obviously works, no HP penalty applied
Jump - works fine, but don't use it for a counter, or for a back attack as the animation is fixed for the normal battle stance
Remember - it seems to work, middle character acts out attack but no visual spell confirmation is used until you see HP/status changes
Sing - game freezes
Medicine - this works with the middle character and the healing heals your characters (which means it targets the enemies by default...), but is factored against magic defense
Build Up - the monster ends up doing nothing and stuck at it...
Kick - works obviously
Twin - monster is stuck... if twins are involved, they go into twin casting mode until a twin is unable to cast the spell (well, the twins are never able to cast the spell in the first place)
Strengthen/Boast - it does work, but the middle character is in the special attack stance instead of the enemy character
Hide - Hide action is acted with the middle character, but then everyone simply dies (I'm serious)
Pray - this works with the middle character and the healing heals your characters (enemies targeted by default) and is factored against magic defense...
Aim - doesn't work.... it had promise too

Cry - it probably works... but it doesn't ever quite make sense to use this... middle character is used for animation
Endure - it works, but it targets one random character by default...
Cover - it works.. middle character acts but it starts forcing Cecil to cover others that are targeted by this... I think Off would actually do the opposite...
Peep - it works... middle character acts and operates exactly like the spell w/o the graphics
Throw/Dart - it won't allow you to target your characters... but amazing you can redirect it to let the enemy kill itself, with no animation (the damage algo is applied to a non-existance weapon power of 0)
Sneak/Steal - you can't steal from characters, but you can let the enemy target itself to get freakish-self-stealing....
Spirit Wave - doesn't work, monster script is stuck
Note: Only the middle character seems to act out the action, and if there is no character there, no visual confirmation is executed...