State-of-the-art requirements modeling tools rely on predefined notations. In contrast, requirements engineers and stakeholders often sketch requirements in arbitrary notations during early elicitation phases. Engineers must then manually transform the sketches into semi-formal models, which is a time-consuming and error-prone task. We propose to investigate how early sketching and the transformation of sketches can be supported by a semi-automatic method that allows engineers to assign meaning to the sketches on the fly. Our tool-supported contribution is supposed to bridge the gap between sketches and semi-formal models.