Shader forge projection

Hi, i want to project and image Downwards with shaderforge, The problem is i want the projection to stop at the first poly it encounters, rather than traveling right through the object and projecting onto the other side as-well.
I am trying to make a snow shader which projects the snow onto a UVed model with it own texture atlas, I don't want to use the model UVs for the snow because that will waste texture space.

 

want something like this
https://www.assetstore.unity3d.com/en/#!/content/14581

I would buy it if it was shaderforge compatable