The secondary use of routinely collected patient data made possible by the broad consent form is seen as a prerequisite for developing data-driven health technologies. In Germany, relevant stakeholder groups (e.g., ethics committees and data protection authorities) specified the broad consent form; however, only one group of patient representatives was consulted, which may indicate asymmetries in engagement. This situation informed our research on medical data donation and emphasized foregrounding patient values. Drawing on participatory design, value sensitive design, and emerging research on value-led participation, we propose a method consisting of (1) a workshop concept for participatory value elicitation composed of four carefully coordinated phases and (2) an analysis procedure to examine the empirical data collected. This analysis allowed us to derive design requirements for medical data donation user interfaces. We conducted three workshops with patient advocates of vulnerable groups and patients in residential care of a psychosomatic unit. Our findings provide new directions to improve user interfaces for medical data donation: First, user interfaces need to enhance patients’ reflective thinking about the potential consequences of their data donation; second, a decision facilitator supporting patients’ value-based decision-making (e.g., by providing simple language or tailoring descriptions to patient needs); and finally, a data intermediary relieving patients’ decision-making and giving them control over their data after donation. Moreover, we emphasize the need to increase the use of participatory approaches in health technology development.