Random Item Damage on Craft/Smelt

Is it possible to give an itemstack a random item damage when it is crafted or smelted?

Right now I've got:

public class CraftingHandler implements ICraftingHandler {
@Override
public void onCrafting(EntityPlayer player, ItemStack stack, IInventory craftMatrix) {
	if (stack.itemID == CivWars.ingotBronze.itemID) {
		stack.setItemDamage(CivWars.rand.nextInt(7));
                }
        }

@Override
public void onSmelting(EntityPlayer player, ItemStack stack) {
	if (stack.itemID == CivWars.ingotBronze.itemID) {
                        stack.setItemDamage(CivWars.rand.nextInt(7));
                }
        }
}

It seems to work, except when you shift-click and that kinda ruins the whole point. Am I doing something wrong or is there another way to do this? Any help would be greatly appreciated.