In addition to established methods, the treatment of mental disorders using Virtual Reality Exposure Therapy is becoming commonplace. We present an approach, which extends this concept in three ways: (1) the provision of maximum control for the therapist over the exposure environment, (2) the inclusion of different media and mediation elements in the virtuality continuum in Mixed Reality, and (3) support for co-located and remote collaboration between therapist and client. This paper gives a brief overview of related work in the field, describes our conceptual approach and a first implementation, and highlights initial findings and issues. Empirical results of our work in progress will be presented at the conference.