Get into a battle with Lloyd as your controlled character, have the Material Blade equipped, and have 1 HP(he doesn't have to have exactly 1 HP, it just makes it easier). Also, make another character Manual so you don't get stuck. Run up to an enemy, and just as they are about to hit Lloyd, press A+B+X to perform Falcon's Crest. If done correctly, Lloyd will die while casting Falcon's Crest. This takes practice and patience. Now, switch the controller to the slot of the character set to Manual and try casting a spell. It won't cast. The effect will wear off after a while. Video here. If Lloyd dies before he casts Falcon's Crest, have Sheena use Purgatory Seal instead of using a Life Bottle, he will be revived with 0 HP, which should speed things up.
Submitted by: Matt