Custom Modding of Zen Cart Shipping Module

hello we cureently use the ceon advanced shipper mod on one of our stores. we need some custom coding done on how the store displays its delivery options. at the moment we have 3 delivery options with all products assigned depending on manufacturer. the problem we have is that we need the module to dynamically put all items on the third delivery option when there is more than one item in the cart. please see spec below :- "If a customer orders more than one product and all products are available on the same delivery method, we do nothing and they would just see the one delivery option with all products grouped against it anyway. If a customer orders more than one product and one or more of them have differing delivery methods (no matter what those methods are), we just show method 20 delivery option as the only one available and group all products against that delivery method." coding should be simple enough using php if statements.