<div id="flexslider-object" class="flexslider">
    <ul class="slides">
        <li><img></li>
        <li><img></li>
        <li><img></li>
    </ul>
    <ol class="flex-control-thumbs">
        <li><a><img></a></li>
        <li><a><img></a></li>
        <li><a><img></a></li>
    </ol>
</div>

$.fn.thumbScroller = function () {
    var div = $(this),
            wrapScreenHeight = div.height(),
            top = div.offset().top,
            $list = div.find('ol'),
            wrapHeight = div.outerHeight(),
            listHeight = div.find('ol').outerHeight() * 1.3;
    $list.on('mousemove', function (e) {
        var cPointY = e.pageY - top,
                dP = ((cPointY / wrapHeight));

        div.animate({scrollTop: (listHeight * dP) - wrapScreenHeight}, 1, "linear");
    });
};
$('#product_slider').thumbScroller();