Allowing 'specials/sales' on OSCommerce

Hello, I am working with an oscommerce site. Right now I have the 'get 1 free' table (it is a contribution on the oscommerce support site) installed and working. However, this table only allows me to get 1 free product and not category. The website sells soaps, oils, and other body products. I want to have a special that allows users to buy any 1 soap and get any 5th soap free. Right now I am able to have it so that if they buy 4 of the same soap they get the 5 (of the same soap) for free. I need someone to change the special so that I can be able to buy 1 'category and not product' and get the 5th product free. I also need that information about the sale to be on the '[login to view URL]' page.