How to render SKinned Mesh By Graphics.DrawMeshNow

I want to outline a charactor, But I dont want to change it's Shader, I Just want to use Graphics.DrawMeshNow() in OnPostRender,but it always seems something wrong here is the code

Code (CSharp):

1. void OnPostRender()
2.     {
3.  
4.         Mesh ms = new Mesh ();
5.         skin.BakeMesh (ms);//bake mesh
6.         mat.SetPass (0);//MyOut Line Pass
7.         Graphics.DrawMeshNow (ms, skin.transform.localToWorldMatrix);
8.     }
9. }

Anyone knows how to fix this?