You could try something like this:
.dropdown-hover .main-navigation:not(.toggled) ul ul li:hover > ul,
.dropdown-hover .main-navigation:not(.toggled) ul ul li.sfHover > ul {
left: 0;
position: relative;
}
.dropdown-hover .sub-menu .dropdown-menu-toggle:before,
.dropdown-hover .children .dropdown-menu-toggle:before {
content: "\f107";
}
However, you’ll notice that the UX suffers when this happens, as the height of the dropdown area jumps around as you move your mouse down the list.