Mirror modifier, but not quite. Is there a phantom modifier? I need help, tried to google and seems I do not google the right keywords.

I need the thing like mirror, but not quite.

I want to mirror specific mesh object few exact places and edit the source mesh and see it reflected 3 other places.

Mirror modifier makes one copy - I need two, and each of them placed somewhere in space. I need that I can change position of each of the "phantom" meshes.

Is there such modifier or approach? 

Any ideas much appreciated,
We'll start with this mesh (I extruded a face so it isn't symmetric):



Go to the object tab and add the object to a group:



Now, create an empty. Go to the object tab and set the duplication to the group you just created:



Now, to mirror the object, simply make the x-scale of the empty negative. It will become flipped. Since Blender is smart enough, the normals will be alright.



Now, you have a flipped copy of the object that will change if you change the original. You can repeat this if you need more copies, and you can position them as you wish: