Abstract— In several contexts, the success of Workflow applications is limited by the excess of rigidity of workflow enactment, which leaves no freedom to end-users to “customize“ processes and process activities to their specific needs. In this paper, we capitalize on a reference model for flexible processes definition and execution that effectively supports the dynamic, user-based management of collaboration processes, and propose an extension based on mashup technologies for accommodating the needs of process actors to self-define and customize their process activities. The resulting approach especially aims at supporting the flexibility required by collaborative processes, where the dynamics through which peers collaborate and coordinate can be difficult to predict in advance.