If you want to call 3 databases at once, you need 3 connections and some sort of event/handler to perform those actions when you say
GoGetBanners() is called then your data access method will know it has to communicate with each server and then merge the results and send them back to you as a single result.
So what I see is a table or config of sorts that holds your connections, you iterate through each of them every time your data access methods are called and simply add any results to a dataset and return that dataset to your business logic with the results of all 3 databases. This would assume you have all the class names the same in all instances of Kentico. Your
GoGetBanners() method could pass in similar parameters as what Kentico accepts, ClassName, Where, OrderBy, etc.