The really nice thing about many shipping modules is that you can DUPLICATE them - or create CLONES of them.
This means that the cloned modules will BEHAVE in exactly the same way as the original module, but that it can be used for different shipping methods and zones.
Here's the technique that can be applied to the FLAT module, but it can also be done with the ZONE and TABLE module.
http://www.zen-cart.com/forum/showpost.php?p=656878&postcount=2
There is a ZONE TABLES module in the free addons that I use a lot, and cloning this module give you a LOT of additional shipping method options.