Giving ISPs more fine-grain control over interdomain routing policies would help them better manage their networks and offer value-added services to their customers. Unfortunately, the current BGP route-selection process imposes inherent restrictions on the policies an ISP can express, making many useful policies infeasible. In this paper, we present Morpheus, a routing control platform that enables a single ISP to realize a much broader range of routing policies without changing the underlying routers or coordinating with other domains. Inspired by multi-criteria decision analysis (MCDA), the design of the Morpheus server allows network operators to easily define new policy objectives, make flexible trade-offs between the objectives, and realize customer-specific policies. We present the design, implementation, and evaluation of Morpheus as an extension to the XORP software router. Our experiments show that Morpheus can support a large number of policies while handling the high rate of BGP update messages seen in large ISPs.