Code

textOnTheRight = new MindFusion.Diagramming.Wpf.Shape(
Shapes.Rectangle.Outline,// reuse the rectangular shape
null,// no decorations
new ElementTemplate[]// define text region
  {
new LineTemplate(32, 29, 90, 29),
new LineTemplate(90,29, 90, 69),
new LineTemplate(90, 69, 32, 69),
new LineTemplate(32, 69, 32, 29)
  },
   FillRule.EvenOdd,// doesn't matter here
   "textontheright"// to access the shape later using Shape.FromId
);