The need for more sustainable solutions makes design an increasingly complex task. New supportive tools and methods are thereby required to stimulate creative thinking to generate new sustainable proposals. Multi-disciplinary design teams need especially in the conceptual design phase more support. Therefore a design method was developed which focuses on the creation of proposals in the conceptual phase of design based on the knowledge and experience of the design team members by using a morphological overview based on the individual morphological chart of design team members. After testing through workshops and trainings in the industry the method was used by students in the course of a two day workshop. Knowing now what is inside the box (the design team's morphological overview), the step was made to support thinking out of the box. The workshops were used to examine the effects of different interventions to stimulate creativity of a design team. In this case, introducing a professional to the student teams at the last session of the workshop and the use of so called C-projectors of the C-K theory by Hatchuel and Weil. It proved that the introduction of a professional had no significant quantitative effect, whereas, the use of the C-projectors led to a significant increase of generated sub-solutions.