It sounds to me like a module setting is all you need. With a module setting you put an instance of your amazon module on the page and set the asin in module settings. Module settings are instance specific so you can even put multiple amazon modules on a page and set a different asin for each one.
My documantation is rather scant but ther is some here:
The second link only touches on it but there is a folder for FeatureDefinitions where you can put config files that define the settings for your feature at setup time, or you can manually add them from the UI under Administration > Advanced Tools Feature Installation
You can study config files for existing features to get the syntax for the config files. You'll find som in /Setup/applications/mojoportal-core/FeatureDEfinitions folder.
Hope it helps,