JavaFX 2.0 :: Bidirectional Binding Text Field / Double Property - Validation Possible?

Is it possible to validate the input of a TextField that ist bound to a Property before both values are updated? Following is an example of my problem .....
 
In my model, there is a SimpleDoubleProperty discount. As you can see, there is some validation logic in the method setDiscount that might be used by other parts of the model.

public class Model {
  private DoubleProperty discount = new SimpleDoubleProperty();
public DoubleProperty DiscountProperty() {
  return discount;
 
[Code] ....
 
My Main class has a Textfield that is bound to the discount-property, a button to put the current value of the discount-property to console and a button to call the setDiscount-method ......

public class Main extends Application {
  @Override
  public void start(Stage primaryStage) {
  try {
  Model model = new Model();
  BorderPane root = new BorderPane();
  Scene scene = new Scene(root,100,100);

[Code] .....

By using the bidirectional Binding between the TextField and the discount-Property, the setter in the model is never called and therefore there is no validation of the input value. When calling the setter programatically with the second button, everything works as expected.
 
I experimented with neglecting the Binding and using ChangeListeners for both the TextField and the discount-Property but only produced infinte loops when both listeners triggered each other alternating.