In Human-centered design the whole system of (human) user and technical product is focused within the design process. Regarding the methodological support, current HCD-methodology supports primary phases of requirement definition and (usability) testing rather than the phase of designing as such. Within the conceptual design phase though, methodology from engineering and industrial design finds application for the development of interaction solution as well. However, this methodology focuses on designing technical product solutions and thus developing a product “around” the user. The user as such is seen as important part of the all-over system but not as partial solution of the whole user-product system. Within this paper an approach is depicted that focuses on the development of physical user (inter) action solutions as partial solutions of the all-over user-product system. By explicitly modeling these user (inter)actions this approach employs effects of externalization and confrontation by solution explication which are used in various conceptual design methods. Within a first design workshop the suggested approach is illustrated before experiences made are summarized and further research ideas are derived.