@skelly solution is good but will not work on mobile devices as the hover state won't work.
I have added a little bit of JS to get the BS 2.3.2 behavior back.
PS: it will work with the CSS you get there: http://bootply.com/71520 though you can comment the following part:
CSS:
/*.dropdown-submenu:hover>.dropdown-menu{display:block;}*/
JS:
$('ul.dropdown-menu [data-toggle=dropdown]').on('click', function(event) {
// Avoid following the href location when clicking
event.preventDefault();
// Avoid having the menu to close when clicking
event.stopPropagation();
// If a menu is already open we close it
$('ul.dropdown-menu [data-toggle=dropdown]').parent().removeClass('open');
// opening the one you clicked on
$(this).parent().addClass('open');
});
The result can be found on my WordPress theme (Top of the page): http://shprinkone.julienrenaux.fr/