The relation between ethnography and design is often discussed in terms of being direct or indirect. The debate on using ethnography in design, models the problem as a matter of mediating between users and designers. This fails to take 'use' serious and renders the problem epistemic i.e. a matter of creating a better understanding or description of the user. Inspired by later developments in Science and Technology Studies I engage an ontological reconceptualization and turn to consider and practice the relation as performative - thus making ethnography, design and users' practices converge. I show this by the case of how the concept of 'medication management' has been performed differently on a combined CSCW and participatory design project in healthcare. It is suggested that through design interventions with working prototypes; prospective analysis and participatory design can be fruitfully assembled in situations of use.