You already know the answer. Continuous refactoring. More problematically, the business rules themselves need to be continuously refactored, which means you ne

You already know the answer. Continuous refactoring. More problematically, the business rules themselves need to be continuously refactored, which means you need the buy-in of the people who hate spending time on refactoring, it's not something you can do behind their backs with padded estimates (not that I've ever seen that actually work out in real life either).