Today, automotive model-driven development is done on the architectural level with AUTOSAR and on lower levels with tools like Matlab/Simulink. Due to strong customization demands, the development has to cope with variability, in general. The used tools provide if ever, just limited variability handling capabilities, especially for handling structural variability. As a result, functionality and variability handling mechanisms are often intermixed in the models. Thus, a clear separation does not exist and recognizing what belongs to one or the other is hard to determine. To overcome this situation, we propose a new concept for Simulink -- termed variable function modules -- that enables the separation of concerns by encapsulating functions and raises the awareness of variability. Furthermore, the concept integrates seamlessly into existing concepts to model variability based on conditional model elements. We show also how the concept can be brought in line with the intrinsic concepts of AUTOSAR.