[BCSE]

I think I have it! I had a few minutes tonight to take a stab at it and seem to have it. It's not completely tested though, so let me know if you find any problems with it.

Here's how to try it:
1. - BACK UP skin1/customer/categories.tpl
- BACK UP include/categories.php

2. Add this code to include/categories.php:

# BCSE Begin
if(empty($subcategories))
{
	$pos=strpos($current_category["category"],"/");

	while(!$pos===false)
	{
		$previous_pos=$pos;
		$pos=strpos($current_category["category"],"/",$pos+1);
	}
	$parent = substr($current_category["category"],0,($previous_pos+$pos));

	if (!empty($parent))
		$cur_dir_len = strlen($parent);

	foreach($all_categories as $all_category) 
	{
		
		$category=$all_category["category"];

		if(!strstr($category,"/")) {

				if(empty($parent)) { 
					$super_subcategories[]=$all_category;
				}
		}

		if(!empty($parent) and substr($category,0,$cur_dir_len+1) == $parent."/" and $category!=$parent) 
		{
			if(!strstr(substr($category,$cur_dir_len+1),"/")) 
			{
				$all_category["category"]=ereg_replace("^.*/","",$all_category["category"]);
				$super_subcategories[]=$all_category;
			}
		}

	}
	
	if(!empty($super_subcategories))
	{
		$smarty->assign("super_subcategory",$super_subcategories);

	}
}

# BCSE End

After:

#
# Put all root categories to $categories array
# Put all subcategories of current_category to $categories array
#
if (!empty($current_category))
	$cur_dir_len = strlen($current_category["category"]);

foreach($all_categories as $all_category) {

	$category=$all_category["category"];

	if(!strstr($category,"/")) {
            $categories[]=$all_category;
			if(empty($current_category)) { 
				$subcategories[]=$all_category;
			}
	}

	if(!empty($current_category) and substr($category,0,$cur_dir_len+1) == $current_category["category"]."/" and $category!=$current_category["category"]) 
		if(!strstr(substr($category,$cur_dir_len+1),"/")) {
			$all_category["category"]=ereg_replace("^.*/","",$all_category["category"]);
			$subcategories[]=$all_category;
		}

}

3. Add this code to skin1/customer/categories.tpl

{* BCSE Begin *}
{section name=super_idx loop=$super_subcategory}
<font class=CategoriesList>{$super_subcategory[super_idx].category_name}</font>

{/section}
{* BCSE End *}

Before:

{/if}
{/if}


{/capture}
{ include file="menu.tpl" dingbats="dingbats_categorie.gif" menu_title=$lng.lbl_categories menu_content=$smarty.capture.menu }

I tested this on 3.5.10. It should work on 3.5.9.

Hope this helps!

Carrie