I found an old post by Dr.Byte here, but I was wondering if there's a way to turning off the module when mixed products are in cart?

I have a very large number of categories and would like to limit moneyorder only to some of it. Dr.Byte's solution is good and it does enable moneyorder when products from those categories are in cart, but I don't want to allow it if there are products from other categories.

Any help would be greatly appreciated.