The use of workflows to support and realize computer simulations, experiments and calculations is well-accepted in the e-Science domain. The different tasks and the parameters of the simulation are therefore specified in workflow models. Scientists typically work in a trial-and-error manner which means they do not know how the final workflow of a simulation has to look like. Therefore, they use a maybe insufficient workflow model as a basis and try to improve this model over multiple iterations to get a better approximation to the problem to solve. So in each iteration multiple trials are based on different variants of the same workflow model. Towards the goal of building variants of workflow models and enabling the reuse of existing scientific workflows in a controlled and well-defined manner, in this paper, we identify how configurable workflow models will support scientists to customize existing workflow models by their configuration. Therefore, we introduce possible configuration options for scientific workflows and how scientists can specify them. Furthermore, we show how configurable workflow models are a first step towards enabling the collaboration among scientists in creating scientific workflows.