WPF How to intercept TabControl SelectionChanged event prior to it occurring?

Question

The approach i've taken is to detect if TabItem HEADER was clicked (and ignore clicks elsewhere).

Attempt 1:

If I hookup a mouse preview event in the TabControl's XAML's

<TabControl PreviewMouseLeftButtonDown = "TabControl_PreviewMouseLeftButtonDown">
<TabItem>
  <TabItem.Header>
    <StackPanel Orientation="Horizontal">
        <Image />
        <TextBlock />
        <TextBlock />
    </StackPanel>
  </TabItem.Header>
</TabItem>
   <TabItem Header="etc" />
   <TabItem Header="blah" />
   <TabItem Header="blah" />
</TabControl>

, the resulting event handler fires every time a click occurs in any element within the TabControl. This is to be expected, due to tunnelling / bubbling etc.

However, i want to detect if a click occurred in the TabHeader region, so i can take special action, and ignore all other cases.

Now in the event handler

private void TabControl_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
}

, none of the parameters sender, e.Source, e.OriginalSource is helpful to say with certainty that i clicked on the tabheader.

Attempt 2:

Moved the wiring of the event to individual TabItems instead of TabControl; Ditto, no joy, the parameters sender, source, etc are similarly useless.

Attempt 3:

Moved the wiring of the event to the StackPanel within the TabItem.

This looked more promising, in that the Preview Down event only occurs on a click to the header, which is just what i want; BUT sometimes the event does not fire, due to styling issues; The StackPanel may not necessarily cover the whole of the TabItem header region ! (And anyway, me thinks any solution dependent on styling would be dodge to the max)

What am i trying to achieve?

I want to intercept the TabControl's SelectionChanged event, prior to it occuring. i.e. in the WinForms world we would probably have some event called TabControl_SelectionChanging. But since in the advanced modern world of WPF /sarcasm there is no such luxury, i had to resort to PreviewMouseLeftButtonDown.

If this can be achieved via fine tuning either of the attempts above, or in some totally new way, please send ideas / code.