1) find a battle
2) go to items
3) select an empty space, and replace it with your weapon/shield
4) when you're done with both hands, fight and let another charecter put nothing in hand
5) finish the battle and re-equip the weapons

NOTE:You'll be holding two of that item. To, use only one, didarm and rearm. No you'll have one weapon in hand and the other in your inventory. This is useful if you need extra money.