Unity 2D Cube Planet Gravity

Hey Community. I haven't found anything about my topic in unity 2D. All I found was 3D (http://answers.unity3d.com/questions/300830/false-gravity-on-a-cube-planet.html) I want to make my Character walk around a 2D Cube. But I can't use Normals in Unity2D for that right? So I have been testing around and I can't find a solution. I have got it to work for round planets but not for cubes. Any suggestions?

Thank you :)