Adding Shadow to Rotoated Matrix Texture

I have a simple shader to rotate the matrix on the fly, but the shadows are no longer rendered on top of it. I do not need to cast shadows with the object, only receive them. If I change the shader to Mobile/Diffuse, it seems to work fine but I lose the rotation effect. How can I render shadows on top of this rotated texture? I have tried using multiple passes but I haven't been able to make it work. I am using one directional light with hard shadows and the plane I have applied this to receives shadows. Here is the shader:

Code (csharp):

1. Shader "Custom/RotateTexture" {
2.     Properties {
3.         _MainTex ("Base (RGB)", 2D) = "white" {}
4.         _Color ("Main Color", Color) = (1,1,1,1) //note: required but not used
5.     }
6.     Pass {
7.         Lighting On
8.         Material {
9.             Diffuse (1,1,1,0)
10.             Ambient (1,1,1,0)
11.         }
12.         SetTexture [_MainTex] {
13.             matrix [_Rotation]
14.             combine texture * primary double, texture
15.         }
16.     }
17.     Fallback "Mobile/Diffuse", 2
18. }