Efficiently incorporating usability and user experience (UX) in agile requirements engineering (RE) remains a challenge. We introduce a team role called ’On-site User Experience Consultant’ (osUX consultant) which supports integrating user-centered design (UCD) firmly in agile RE under the constraints of fixed-price software development projects. Our experience shows that such changes in processes cause tensions. These tensions can arise around issues such as the power dynamics within the team, budgets as well as effectively using insights gained from usability tests. We name methods and practices of osUX consulting and how they fit into different phases of an agile RE process. Additionally, we discuss who within a team is ideally suited to occupy this role. Finally, we describe how old habits in the development process have to be adapted to establish this approach within the project team and with the client.