Service composition is a well-established field of research in the service community. Services are commonly regarded as black boxes with well-defined interfaces that can be recursively aggregated into new services. The black-box nature of services does not only include the service implementation but also the middleware and hardware to run the services. Thus, service composition techniques are typically limited to choosing between a set of available services. In this paper we keep the black-box nature and the principle of information hiding for the service implementation, but break up services vertically. By introducing vertical service composition, we allow services to be provisioned on the right middleware when they are requested, thus making service-binding more powerful as services with the desired quality of service can be provisioned on demand. We introduce the concept of vertical service composition and present an extension to an enterprise service bus that implements the concept of vertical service composition by combining concepts from provisioning with those of (dynamic) service binding.