Hey, now that I think about it.
Have you tried to make the mesh Stationary?
Meshes, same as lights, can be Static, Stationary and Movable.
By default the meshes are set in Static, what generates them a light map.
But you can set a mesh to be Stationary and in that way, it will not generate a Lightmap but it will generate shadow in another objects.
Otherwise, if they are Movable they will not generate even shadows.
I hope this helps you!