The paradigm of automated e-service composition through the integration of existing services promises a fast and efficient development of new services in cooperative business environments. Although the "why" part of this paradigm is well understood, many key pieces are missing to utilize the available opportunities. Recently "e-service communities" where service providers with similar interests can register their services are proposed towards realizing this goal. In these communities, requests for services posed by users can be processed by delegating them to already registered services, and orchestrating their executions. We use the service framework of the "Roman" model and further extend it to integrate activity processing costs into the "ad hoc" delegation computation. We investigate the problem of efficient processing of service requests in service communities and develop polynomial time ad hoc delegation techniques guaranteeing optimality.