如何用鼠标位置覆盖bootstrap工具提示

Question

<a href="#" class="spot ico_1 glyphicon glyphicon-map-marker" data-toggle="tooltip" data-placement="top" title="Dummy Text"></a>

$(".spot").mouseover(function(){
   var x = $(this).position();  
    var topval = x.top;
    var leftval = x.left;        
    $(this).attr("title", "X= "+topval+" "+"Y= "+leftval);      
});

如何用jquery中的xy值覆盖bootstrap工具提示文本？请帮忙