In this paper, a model inversion approach is presented that can be used particularly in cases, where the links between subsystems are hard or even impossible to express within the framework of differential flatness. To overcome this problem, i.e. to establish a link between the desired physical output and the flat output, properties inherent to flat systems are utilized. The method is called flatness-based state decomposition and is applied to a magnetic flux-channel model, within an electromagnetic-mechanical solenoid valve model. This approach shows excellent performance in simulation and has been integrated in the well-established flatness-based optimization scheme for feedforward trajectory generation.