Hi!
FusionMenu supports this feature but there's no option for it in the Gantry Menu widget settings. Please try this, open up your_theme/html/gantrymenu/themes/gantry_fusion/layout.php. This file does the work of rendering the menu and menu items and also adds the Fusion's scripts and stylesheets to the page. Find this line:new Fusion('ul.menutop', {
where it outputs the JavaScript codes to call the FusionMenu. Now add this below that line:direction:{x:"right",y:"up"},
and now your menu flies upward.