[gb2world]

You should be able to do it using smarty or php.

In smarty:
Your subcategories are in this array: $subcategories
number of items in the array: {$subcategories|@count}
You can set smarty variables to determine the subcats per column:
{assign var="subcats_count" value=$subcategories|@count}
{assign var="subcats_per_section" value=$subcats_count/4}

You can create loops in smarty using the variables to get the desired outcome. You can set a variable inside your loop to count where you are, and when you reach the desired subcategory count, you can start a new unordered list.