如何在Silverlight/WPF中反转剪裁几何？

<Grid>
    <Grid.Clip>
        <RectangleGeometry Rect="0,0,100,100">
            <RectangleGeometry.Transform>
               <TransformGroup>
                   <ScaleTransform ScaleX="-1" ScaleY="1" />
                    <RotateTransform Angle="0" />
                </TransformGroup>
            </RectangleGeometry.Transform>
        </RectangleGeometry>
    </Grid.Clip>
</Grid>

<Grid>
    <Grid.Clip>
        <PathGeometry>
            <PathGeometry.Figures>
                <PathFigureCollection>
                    <PathFigure StartPoint="0,0">
                        <PathFigure.Segments>
                            <PathSegmentCollection>
                                <LineSegment Point="100,0" />
                                <LineSegment Point="100,100" />
                                <LineSegment Point="0,100" />
                            </PathSegmentCollection>
                        </PathFigure.Segments>
                    </PathFigure>
                </PathFigureCollection>
            </PathGeometry.Figures>
        </PathGeometry>
    </Grid.Clip>
</Grid>

<Grid>
    <Grid.Clip>
        <CombinedGeometry GeometryCombineMode="Exclude">
            <CombinedGeometry.Geometry1>
                <RectangleGeometry Rect="0,0,100,100" />
            </CombinedGeometry.Geometry1>
            <CombinedGeometry.Geometry2>
                <EllipseGeometry Center="50,50" RadiusX="50" RadiusY="50" />
            </CombinedGeometry.Geometry2>
        </CombinedGeometry>
    </Grid.Clip>
</Grid>