More and more legal norms directly target software-based systems. Although these norms often require some form of legal assessment, such as the data protection impact assessments mandated by the General Data Protection Regulation, they are usually conducted in separated steps before or after development. As legal norms translate to requirements of the system to be developed, they have a profound influence on the software design and architecture, which makes subsequent changes cost intensive. Therefore, it should be ensured that software architects are provided with knowledge that supports them in designing legally compliant systems. In this paper, we derive challenges for legal knowledge transfer and discuss how we address them. As an initial approach, we define a metamodel for structured legal comments and present a first attempt to automatically annotate them within data flow diagrams. The approach is demonstrated with an example system in a real-world legal context, illustrating why supported knowledge transfer is necessary.