The visibility series attribute allows you to create a hidden series inside of a plot. This hidden data can be predefined, but will not be visible until the property is altered from script. 

In the example below, the data inside of the second series is not visible until the button is pressed.

<xyPlot name="examplePlot">
    <data>1 6; 5 4; 9 8; 14 10</data>
  <series name="series2" visible="false">
    <data>2 4; 4 9; 8 1; 12 7</data>

<button content="Show Series">
    examplePlot.series2.Visible = true