Make material always culled.

If you don't want any attempt at rendering it at all:

You can disable any component attached to a game object by setting the enabled property to false.

 gameObject.GetComponent<Renderer>().enabled = false;

If you still want the camera to attempt to render it:

You can change the Alpha of a material's color to 0 (transparent):

 someMaterial.color.a = 0;

Sources:

http://docs.unity3d.com/ScriptReference/Material-color.html

http://docs.unity3d.com/ScriptReference/GameObject-renderer.html