Yep, you could use some additional CSS to float the items and set them fixed width (the LIs) and also set a fixed width for the sub menu (the UL) – e.g. something like this:
#main-menu ul.columns-2 {
width:500px !important;
max-width:none !important;
}
#main-menu ul.columns-2 > li {
float:left;
width:250px !important;
}
and then you just need to set the class to the sub menu you like:
<ul class="columns-2"> ...
By tweaking the widths, you can get as many columns as you like.
