Hey,
I have the same requirements for my app, looked at the link you provided and found a solution:
Create a custom StyleSelector for you chart. Inside the SelectStyle override method access the DataObject that you provide via a Binding to the ItemsSource of your PieSeries like this:
var color = ((SimpleTimesheet.Portable.ViewModel.ChartItem) (((Telerik.Charting.DataPoint) (item)).DataItem)).Color;
and just return a new Style with the color from your Databound Object:
var style = new Style(typeof(Path));
style.Setters.Add(
new Setter(
Shape.FillProperty,
new SolidColorBrush(color.ToMediaColor())
));
return style;
Hope this helps. Let me know if you need an example.
Best
Till