Specification of systems in a software product line (product-line members) is often supported by domain-specific languages (DSLs) that provide powerful language abstractions for selecting the features of the desired system. In this paper, we show that efficient composition of system specifications (which, in our case, are expressed as models) is also possible using (i) a domain-specific workflow model that guides the composition and (ii) a set of domain-specific templates for model transformations. We illustrate the entire approach on a product line for versioning systems, define a metamodel for workflow models and postulate a measure for estimating the benefits of the proposed approach.