This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
You as the architect can change your domain model to reflect a solution designed to solve all use cases. Do not forget to document the reasons.
Remember, the assignament may be missing a lot of information in which you will have to assume in order to develop and deliver your proposed solution.