: Participatory design and model-based approaches are two major HCI design approaches. Traditionally opposed, the first ones promote user's creativity while the second ones support a more systematic approach of the design space. In Mixed Reality domain, combining these two aspects is especially crucial in order to support the design and to help the users to take into account the wide variety of emerging technologies. We introduce in this paper a solution to bring these two approaches together. In addition, we illustrate how the outcomes of this combination of formal and informal approaches serve as input for the implementation of the designed solution. Key words: design method, mixed reality, focus group, UI modelling, software modelling