WPF expander toggle button placed between header and content

I have expander control with header containing 3 vertical labels.

For expand direction 'Down', the toggle button appears on left and vertical central to the Header (pic1)

Now for Expand direction to 'Right', the toggle button appears on the top of the header (pic2), how can I place the toggle button on the right side of Header? (in the way of expansion)

<Expander Grid.Row="1" ExpandDirection="Right"><Expander.Header><Border BorderThickness="2" BorderBrush="Black"><StackPanel Orientation="Vertical"><Label>header label1</Label><Label>header label2</Label><Label>header label3</Label></StackPanel></Border></Expander.Header></Expander>

sri