You could just call the draw() method on the group to which you added the shape. This will only redraw the shapes in that specific group. I.e. textGroup.draw()
In fact you can call the draw() method from any Node (including, Shapes, Layers, Stages, Groups etc).
Update
I made a fiddle http://jsfiddle.net/u9xHe/1/. Adding a Text shape, calling draw, then adding another Text shape and calling draw again. Nothing seems out of place in this case.