Programming robots presents significant challenges, including high costs, extensive time commitments and steep learning curves, particularly for individuals lacking technical background in engineering. These barriers have been partially mitigated by the emergence of end-user development methodologies. Yet existing approaches often fall short in equipping users with the necessary software engineering competencies to develop comprehensive robot behaviors or to effectively maintain and re-purpose their creations. In this paper, we introduce a novel end-user development approach designed to empower physical therapists to independently specify robot-assisted physical training exercises, eliminating the need for robotics experts' intervention. Our approach is based on a set of design goals obtained through a participatory design study with experts in the field. It utilizes a textual domain-specific language (DSL) that enables users to define expected robot behaviors through Behaviour-Driven Development (BDD) scenarios. This paper discusses key themes, design objectives, and the evolution of requirements that emerged from an evaluative workshop.