Lighting for side section view

Hello All,

I have a 3D cross-section scene which has several tunnels on top of eachother and open land, shown in isometric view. I am using directional light for lighting the land but then every level is casting shadow to the level below. I want the shadows but not from upper tunnels, which wouldn't happen in reality. I am using a colourful low poly design and I want everything visible and well lighted. What is a good lighting solution for a mobile game in this setup?

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