In Dashboard Menu, go to Custom Header and add the following code.
<script type="text/javascript">
$(function(){
//iterate thru iframe elements
//$("iframe").each(function(){
//wait for iframe to load is a better idea
$('iframe').on('load', function(){
$(this).contents().find("a").attr("target", "_top");
});
});
</script>
Every link found in the portlet will now open in the parent frame. You may adjust the code accordingly to suit your needs.