1 Mesh, 1 Material 2 UV channels 1 Normal map?

Hi Everyone,

I'm having some issues with applying a Normal map to a mesh in Unity with only 1 material. I've attached some images to give you an idea of what I'm talking about.

I have a sofa model and basically, I'm trying to have only the areas marked in green using the Normal map, the other areas in grey were made using the automatic UVW modifier in 3DSMax, and don't need any details, (this was done to save time/texture space on the Normals).

I was wondering if it's possible to use UV channels to achieve the desired result? Currently, the normal maps just apply to all aspects of the model, again what we want really is to have only one material for our pipeline, and preferably done so using the standard shader.

It might be a long shot but a colleague was able to achieve something similar but we haven't been able to recreate the results. Any help would be greatly appreciated.

Thanks, Tim