Specular only lights

I baked the illumination of my 3d models using an external 3d software, and now I would like to insert a realtime light in Unity that not affects the illumination, but only the specular highlights.

I use a directional light with shadow off, but to obtain a specular highlight I need to raise up the intensity value, and it affects the illumination of my objects.

I'm using the standard Unity shader for all my objects, because I need an Albedo texture, a second Albedo texture for my baked illumination, and a normal map. I need to modify this shader? (I have not experience in shader editing...)