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Composition of Web services helps to lower the time-to-market of service-based applications by reusing the functionality provided by services that are already deployed at geographically distributed locations. Due to the diversity of services, the client acceptance of new applications is determined more and more by non-functional aspects, such as Quality of Service, or cost. The throughput, response time, and communication cost of composite services depend on the characteristics of each component service involved, as well as on the manner these components are tied together. Research has shown that distributed data-flow models can offer better performance and lower communication costs in service composition than centralized models. However, an impediment towards data-flow distribution in Web services composition is that the component services cannot exchange data directly without central mediation. We propose therefore a non-intrusive approach for achieving data distribution among Web services that are engaged in composition, bringing minimal extensions to the underlying middleware and not tightening the coupling between them.