Well, if anyone is interested here's my hack to get this to work. I set a counter var and increment with each iteration of createChildren. I'm sure there's a more effecient or "correct" way, so if anyone knows please share.
public class CpPiechartLegendItem extends LegendItem { public static var item_index:Number = 0; public function CpPiechartLegendItem() { super(); } override protected function measure():void { super.measure(); } override protected function createChildren():void { super.createChildren(); trace(super.source.dataProvider[item_index-1].myProperty;); } protected override function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void{ super.updateDisplayList(unscaledWidth, unscaledHeight); } }