Horizontal Drop Menu sort order of mega-menu

I'm using the alternate ul generator from horizontal dropdown menu by get em fast. I'm wondering if anyone would know how to sort the categories submenu in alphebetical order vertically rather than horizontally? I looked through the categories_ul_generator.php but my inability to understand php got me lost pretty quick.

That would probably be very complex. You can't just sort vertically; you would have to sort horizontally and then put the items in an n-by-n array and flip it rows-for-columns (something I don't have practical experience with), and that might still mess up if there are sub-subcategories in the dropdown.
The other possible approach, which actually has a chance of working in likely situations, would be to insert div wrapper tags into the final output string every so many items (calculated to yield the desired number of divs), and then give the divs a width and float them left so they sit side by side. My String Replace at Intervals mod in Free Addons can help with this. It is discussed in a forum thread where I worked out its base code with a poster developing a mega-menu display.

Obviously one of those things that sounds simple in lay terms...

A very tedious method you could use without new coding would be to give sort orders to the subcats so that they end up appearing as if they are sorted in columns. This would, however, cause odd sorting in other displays than the mega menu, if you have any other displays.