Transparent with Specular Only shader

I'd like to have a shader that only shows the spectacular or highlights. No diffused colour at all. Is this possible?

It would be like a cheap glass material, no reflections just a coloured highlight (default white) but not using any rgb to multiply the specular.

I have eyes that have a have a eyeball outer which is used for highlights only. In a 3d rendering the ambient and diffuse is usually set to black, spec to white.