Here's an idea: the ability to change render options.
Here's how it would work: you select the solid, and there's a little gear in the top right. It would contain the lock and hide features as normal, but there's an extra item: render options. When you click it, you are presented with a list of the shaders already in use for the solid. By default, there would be the Lambert material, and the Basic backside wireframe material that you already use for everything. You would have the option of removing, adding, and editing materials at will. Then, you could include these in the MTL when the user exports as .obj.