unity3d中 如何用js代码来更改shader中的3个子着色器

Question

#pragma strict
var alpha;
var fadeSpeed : float=10;
var timeLeft:float=10;
var rotationSpeed:float = 100.0f;

function Start () {

}

function Update () {
transform.Rotate(Vector3(0,rotationSpeed*Time.deltaTime,0));

if (gameObject.renderer.material.color.a > 0)
{
    timeLeft = timeLeft - Time.deltaTime;
    alpha = (timeLeft/fadeSpeed);
    gameObject.renderer.material.color.a=alpha ;
    gameObject.transform.position.y+=0.002;

}

}
利用上面的代码只能改变Material中Element 0，改变不了element2，element3