Modelling can be applied to all aspects of healthcare systems but one area in particular, clinical pathways, are of great interest currently due to many flow-oriented issues that are well-documented in the media. These pathways typically describe sequences of sorting and treatment activities such as surgical procedures or the care process for managing injuries, for example bone fractures. Previous efforts in using modelling languages have not been promoted as being highly generalizable nor have emphasised the inclusion of constraints defining rules for particular treatment activities. In this paper, we propose a workflow for building flexible models for healthcare systems by exploiting the combination of UML, OCL, and SMT solving. This paper serves as an exposition of an idea that can be developed into a more complete framework that could be used to create workflow models for improving the efficiency and safety of more complex clinical activities. A good application would be to tackle the prevalent problems of emergency departments and some of the challenges in this respect are discussed.