public class GraphicsLayerCreationParams : LayerCreationParams 

{
  if (map.MapType != MapType.Map)
    return;// not 2D

  var gl_param = new GraphicsLayerCreationParams { Name = "Graphics Layer" };
  // Note: must be called on the QueuedTask
  {
    //By default will be added to the top of the TOC
    graphicsLayer = LayerFactory.Instance.CreateLayer<ArcGIS.Desktop.Mapping.GraphicsLayer>(gl_param, map);

    //Add to the bottom of the TOC
    gl_param.MapMemberIndex = -1; //bottom
    LayerFactory.Instance.CreateLayer<ArcGIS.Desktop.Mapping.GraphicsLayer>(gl_param, map);

    //Add a graphics layer to a group layer...
    var group_layer = map.GetLayersAsFlattenedList().OfType<GroupLayer>().First();
    LayerFactory.Instance.CreateLayer<ArcGIS.Desktop.Mapping.GraphicsLayer>(gl_param, group_layer);

    //TODO...use the graphics layer
    //

    // or use the specific CreateGroupLayer method
    LayerFactory.Instance.CreateGroupLayer(map, -1, "Graphics Layer");
  }
}