A fundamental principle of service oriented architectures is the decoupling of service requesters and service providers to enable late binding of services at deployment time or even dynamic binding of services at runtime. This is important in enterprise settings, where different services that implement business functions in critical business processes are dynamically chosen based on availability or price. The same problem also applies to dynamic Grid environments where resources need to be dynamically chosen based on availability and other non-functional properties. The WS-Policy framework describes how policies for both providers and requesters are specified to allow the selection of services based on these policies. Existing approaches, using WS-Policy, have drawbacks by placing the burden of the service selection partially on the client. In this paper we present an approach to extend an enterprise service bus that allows service clients to submit policies the service provider needs to comply with directly in the message that triggers the service invocation. We show how these policies are evaluated in the bus and how policies are defined for not only stateless services, but also stateful resources.