You could edit event.chartX after coordiantes are found in each chart by adding:

event.chartX = (event.chartX+600) % 200;

Adding 600 to avoid negative values and % by 200 because each chart has 200px of width. Example: http://jsfiddle.net/fzda6z8p/

Relevant part of code:

$('#container').bind('mousemove touchmove touchstart', function (e) {
    var chart,
        point,
        i,
        event;

    for (i = 0; i < Highcharts.charts.length; i = i + 1) {
        chart = Highcharts.charts[i];
        event = chart.pointer.normalize(e.originalEvent); // Find coordinates within the chart

        event.chartX = (event.chartX+600) % 200;

        point = chart.series[0].searchPoint(event, true); // Get the hovered point
        if (point) {
            point.highlight(e);
        }
    }
});