private static void IsDefaultChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args)
    {
        if ((bool)args.NewValue)
        {
            Window.Current.CoreWindow.KeyUp += CoreWindowOnKeyUp(dependencyObject);
        }
        else
        {
            Window.Current.CoreWindow.KeyUp -= CoreWindowOnKeyUp(dependencyObject);
        }

    }

    private static void CoreWindowOnKeyUp(CoreWindow sender, KeyEventArgs args, DependencyObject dependencyObject)
    {
        ((ICommand)dependencyObject.GetValue(Button.CommandProperty)).Execute(null);
    }

HashTable<DependencyObject> current = new HashTable<DependencyObject>();

// Bound as before
private static void IsDefaultChanged(
    DependencyObject dependencyObject,
    DependencyPropertyChangedEventArgs args)
{
    if ((bool)args.NewValue)
        current.Add(dependencyObject);
    else
        current.Remove(dependencyObject);
}

// Permanently bound, once.
private static void CoreWindowOnKeyUp(CoreWindow sender, KeyEventArgs args)
{
    foreach(var do in current)
    {
        ((ICommand)do.GetValue(Button.CommandProperty)).Execute(null);
    }
}

private static void IsDefaultChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args)
{
    var func = (object sender,KeyEventArgs e) =>
    {
         ((ICommand)dependencyObject
             .GetValue(Button.CommandProperty)).Execute(null);
    };
    if ((bool)args.NewValue)
    {
        Window.Current.CoreWindow.KeyUp += func;
    }
    else
    {
        Window.Current.CoreWindow.KeyUp -= func;
    }

}