While there's no out-of-the-box way to accomplish this, you can use FillSceneGraph event to draw custom labels and lines on the chart. Here's a quick sample:

            Line endLine = new Line(new Point(b.rect.Right, b.rect.Bottom), new Point(b.rect.Right, (int)yAxis.MapMinimum), new LineStyle(LineCapStyle.NoAnchor, LineCapStyle.NoAnchor, LineDrawStyle.Dash));
            endLine.PE.Stroke = Color.Magenta;
            labels.Add(endLine);
            Text endLabel = new Text();
            endLabel.SetTextString(dates[1].ToShortDateString());
            endLabel.SetLabelStyle(labelStyle);
            labelSize = Platform.GetStringSizePixels(endLabel.GetTextString(), labelStyle.Font);
            endLabel.bounds = new Rectangle(b.rect.Right, (int)yAxis.MapMinimum, (int)labelSize.Height, (int)labelSize.Width);
            labels.Add(endLabel);
         }
      }
   }

   foreach (Primitive p in labels)
   {
      e.SceneGraph.Add(p);
   }
}