Software Product Line Engineering (SPLE) defines processes to facilitate the development of a family of products in a pre-defined market more effectively. Its success depends on implementation of these processes utilizing best practices with proper tool support. This paper describes how to enhance domain design and variation management processes of SPLE with a domain-specific language (DSL), namely "Kutulu". It also introduces novel modeling tools and dependency injection-based realization approach that are well-suited for product derivation in SPL. Our DSL definition, developed tools and their position in the product line context are put forth in this paper.