The wpf framework does not allow a binding in the CommandParameter because the Binding object is not a DependencyObject and the CommandParameter property is not a DependencyProperty. Perhaps you can simply attach an event handler to the MouseLeftButtonDown event of the series, set the IsHitTestVisible property of the series to true and in the event handler get the original source, get its data context (which is a DataPoint) and get the DataItem (which is the actual business item). Let us know how it goes.
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