Simple emission shader for beast lightmaps

I need a simple shader that displays a model with vertex colors, and emits that vertex color for use when lightmapping with beast.

So far I got this, but it only emits white color, not any of the vertex-colors added to the model.

Shader "Self-Illumin/Vertex Color" {

    Properties {
        _EmissionLM ("Emission (Lightmapper)", Float) = 1
    }

    SubShader {

        Tags { "RenderType"="Opaque" }
        LOD 200
        
        CGPROGRAM
        #pragma surface surf Lambert

        struct Input {
            float4 color : COLOR; // Get vertex color
        };

        void surf (Input IN, inout SurfaceOutput o) {
            o.Albedo = IN.color.rgb;
            o.Emission = IN.color.rgb; // Always results in white?!?
        }

        ENDCG

    } 

}

What am I doing wrong here?

Also, Is this shader really that simple? I mean, the only reason its even a surface shader is that I need to emit light from it. Otherwise a vertex color only shader would work fine. Is there perhaps a way I could tell Unity to bake using one shader, and then swap that shader for a simpler one when actually playing?

Thanks!

Maybe this will help: Lightmapper with custom shader Emission Map - Unity Answers