Remove product listing from categories page

[Webcraft]

I have a client who has created a lot of categories and sub-categories and does not want any products to list in a category with sub-categories - how can I do this?

 

(Perhaps to express this a little more clearly - they do not want pages with listings of sub-categories and products - each page will either list sub-categories or whenit is at the bottom level it will only list products)

 

I've searched the forums but can;t find anything - thanks in advance