Looks like the only way, to me, is to take the specular output from a Tangent V node and using a mix node to add it to another object sans specular component.
Hi. Yes, this is sadly the way Blender works right now (might be a bug, have not checked). The artifacts are based on the meshes geometry, it treats it as a flat shaded object when it calculates the ray shadows. Because of this I found that if you are able to - that the object is not to big, is not the main subject and taking up most of the picture, your computer has enough ram, etc - you can just up the render levels on the objects subsurf modifier if it has one. That will result in a smoother shadow boundary.