Improving the Thesis built-in dropdown menu via javascript

The dropdown menu that Thesis creates is 99% fine, except that it's very unforgiving to users that don't master the use of mouse very easily - old people and people with average to bad vision. I would like to improve its usability using a bit of javascript, allowing the mouse to be a few pixels offside and still keep the submenu open. I tried this in my custom javascript file:

var hoverConfig = {    
         over: function(e){
                e.preventDefault();
                $.log("launch menu");
                $('.sub-menu',$(this)).show();
        },  
        timeout: 500, // number = milliseconds delay before onMouseOut    
        out:  function(e){
                e.preventDefault();
                $.log("hide menu");
                $('.sub-menu',$(this)).hide();
        } 
    };

    $('.sub-menu').hide();
    $("#menu-main-menu").hoverIntent( hoverConfig );

Firebug logging shows that it works - the show and hide functions are called, but the CSS behaviour still triggers and i don't manage to cancel it so that the javascript behaviour takes the full control. Any idea how i can do that?