ElementStacks

HTML

<script src="http://highcharts.com/js/testing.js"></script>
<div id="container" style="height: 400px; width: 500px"></div>
<div id="legend-tooltip"></div>

JavaScript

var chart = new Highcharts.Chart({
    chart: {
        renderTo: 'container'
    },  
    series: [{
        data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0]
    },{ 
        data: [135.6, 148.5, 216.4, 194.1, 95.6, 54.4]
    }]
}, function(chart){
    $.each(chart.series, function(i, serie){
        serie.legendItem.on('mouseover', function(){
            $('#legend-tooltip').text(serie.name);
        });
    });
});