There should be a random start rotation and a rotation velocity parameter in the ParticleMaterial's options, which should be enough for what you are trying to do. You can also set minimum and maximum rotation to 360 to rotate it 360 degrees, but I am not sure why you would rotate them 360 degrees. Perhaps you meant 180?
Also if you still want to use a shader with the ParticleMaterial there is a next pass material in all materials (or just shader ones I don't remember), but I am not sure that it won't duplicate the meshes.