Add a mask to the Text node.
For this example we need a Polygon mask, but you could use a Rectangle, Circle, BSpline etc… if it works for your clip.
Select the Polygon node and draw a mask around your object.
You can invert the mask if you need to see what you are doing, or you can simply disconnect the Polygon from the Text node and draw your mask.
Then connect it after your mask is closed.
You will probably need to INVERT the mask to get the effect you want, but it depends on what you are trying to do.
Watch the video to see it in action.