Product derivation is the process of constructing products from the core assets in a product line. Guidance and support are needed to increase efficiency and to deal with the complexity of product derivation. Research has, however, devoted comparatively little attention to this process. In this paper we describe an approach for supporting product derivation. We show that variability models need to be prepared for concrete projects before they can be effectively utilized in the derivation process. Project-specific information and sales knowledge should be added and irrelevant variability should be pruned. We also present tool support and illustrate the approach using examples from ongoing research collaboration.