I'm looking for a solution to highlight slice of a pie chart only on click

What I have right now is a listener in the series section of my chart:
Code:
                    series: [{
                            type: 'pie',
                            field: 'Count',
                            showInLegend: true,
.....
                            highlight: false,
                    listeners: {
                                itemmousedown: function (obj) {
                                    if (storeData.count() > 1) {
                                        Ext.apply(this, {
                                            highlightCfg: {
                                                segment: {
                                                    margin: 20
                                                }
                                            }
                                        });                                        
                                        this.highlightItem(obj);                                        
                                    }
                                }
                            }
but it's not working!

How can I highlight slices on click

PS: I also tryed this.highlightItem() who is supposed to hightlight the whole series, but it's not working!

Thanx

Phil