HOw to position the start angle of child in customer cirlce panel

Dear all,

I am using this approach to display child item in circle as state in this exemple :

http://www.codebullets.com/custom-circle-panel-wpf-part-1-216

But the thing I am trying to do is that I would like to be able to freely select the starting angle position of child element.

For instance, If I have 4 button to be displayed, I would like to get them align inside the 270°
-0° quadran, sarting at 270°.

IN an other scenario I woiuld like to display them in the 180°-270° strting from 180°

I would like to be able to change it as a property of the Cricle panel.

How can I achiev this ?

regards