Change light direction in SS

I am trying to make a Surface shader that uses a directional light with it's lightDir angle xyz properties defined from the shader properties as a Vector property rather than using the main directional light in the scene. The reason for this is I want the shadows to derive from the scene's main directional light, but the actual light applied to be coming from a different custom angle. Is this possible? What I am having initial difficulty on is figuring out how to convert my customLightAngle vector into the correct object/ world space so I can pass it into the surface shader. Thanks for any pointers.

Code (csharp):

1. vec ("customLightAngle", Vector) = (45,45,45,1)
2.  
3.  
4. fixed4 CustomLight (SurfaceOutputCustom s, fixed3 lightDir, fixed atten)
5. {  
6.     lightDir = myCustomVector;
7.     fixed diff = max (0, dot (s.Normal, lightDir.xyz ));
8. }

 

Here is what I have so far. Still can't figure out how to correctly turn a property vector into a directional light with rotation defined by the vector's xyz.

Code (csharp):

1.   Shader "CustomVectorLight" {
2.     Properties {
3.       lightDirVec ("light vec", Vector) = (45,45,45,1)      
4.     }
5.     SubShader {
6.      Tags { "RenderType" = "Opaque" }
7.    
8.       CGPROGRAM
9. #pragma surface surf CustomLight vertex:vert target 2.0  
10.     struct SurfaceOutputCustom {
11.     fixed3 Albedo;
12.     fixed3 Normal;
13.     fixed3 Emission;
14.     half Specular;
15.     fixed Gloss;
16.     fixed Alpha;
17.     fixed3 CustomLightDir;
18. };
19.     float3 lightDirVec;
20. fixed4 LightingCustomLight(SurfaceOutputCustom s, fixed3 lightDir, fixed atten)
21. {
22.     fixed4 c;
23.     c.rgb = max (0, dot (s.Normal, s.CustomLightDir.xyz ));
24.     c.a = 1;
25.     return c;
26. }
27.    
28.       struct Input {
29.       float2 uv_Tex1;
30.       float3 lightDirVec;  
31.       };
32.      
33. void vert (inout appdata_full v, out Input o) {
34. float3 objSpaceLightPos = mul(_World2Object, float4 (lightDirVec,1)).xyz;
35. objSpaceLightPos = objSpaceLightPos.xyz * unity_Scale.w - v.vertex.xyz;
36. TANGENT_SPACE_ROTATION;
37. o.lightDirVec = mul (rotation, objSpaceLightPos);
38.       }
39.  
40. void surf (Input IN, inout SurfaceOutputCustom o) {
41.       o.CustomLightDir = IN.lightDirVec.xyz;
42.       o.Albedo = .5f;    
43.       }
44.       ENDCG
45.     }  
46.   }