The recent increase in popularity of Storage-as-a-Service cloud solutions influences the way scientists are managing their data. More and more academic groups store and work on their data outside the university domain. Hence, data aggregation and metadata management is becoming increasingly important. While most cloud storage systems offer convenient access APIs, they are rarely fully compatible with each other. This makes migration between backends, or integration of data located in various places, more complicated. A common answer to this vendor lock-in problem lies in adopting common standards. Although there are no commonly adopted standards for cloud storage, yet, the potentially most promising direction at the moment is SNIA's Cloud Data Management Interface (CDMI), which defines the semantics of handling data objects and the required metadata. In this paper we present our prototype implementation of CDMI-compatible proxy, which offers a transparent integration layer on top of both cloud systems and local storage infrastructures. The work is being conducted as part of the FP7 project VENUS-C and released under an open-source license.