powerpoint programmatically add textbox animation triggered by bookmark in mediaobject

I am trying to programmatically add an fade effect on a textbox which is triggered by a bookmark in a mediaobject, eg movie. 

So when the movie plays and reaches the bookmark the textbox will appear with the fade effect.

I have gotten as far as being able to add the textbox to the slide and adding the bookmarks to the mediaobject shape eg using the following code

Now where am I supposed to add the fade effect? VSTO or vba code will really help! this is all in office 14

var application = Globals.ThisAddIn.Application;

PowerPoint.Slide activeSlide = application.ActiveWindow.View.Slide;

PowerPoint.Shape selectedShape = application.ActiveWindow.Selection.ShapeRange[1];

selectedShape.MediaFormat.MediaBookmarks.Add(2000, "Bookmark A");

selectedShape.MediaFormat.MediaBookmarks.Add(5000, "Bookmark B");

selectedShape.MediaFormat.MediaBookmarks.Add(9000, "Bookmark C");

PowerPoint.Shape textBox1 = activeSlide.Shapes.AddTextbox(Office.MsoTextOrientation.msoTextOrientationHorizontal, 0, 0, 500, 50);

textBox1.Name = "TextBox1";

textBox1.TextFrame.TextRange.InsertAfter("TextBox1 text");

PowerPoint.Shape textBox2 = activeSlide.Shapes.AddTextbox(Office.MsoTextOrientation.msoTextOrientationHorizontal, 0, 30, 500, 50);

textBox2.Name = "TextBox2";

textBox2.TextFrame.TextRange.InsertAfter("TextBox2 text");