Create a different subcategory.html file for the home page (subcategory_home.html).
The list of categories is created in sub site_html_print_cat
You can pass it an additional parameter to determin which template to use (simimlar to the dynamic parameter) or you can create a new routine: sub site_html_print_cat_home, and change the call to subcategory.html to subcategory_home.html.
Which is better for you is up to you.
http://www.postcards.com FAQ:
http://www.postcards.com/FAQ/LinkSQL/