Given the increased competitiveness of the business environment, organizations strive to constantly adapt their business processes and supporting tools while maintaining the skill level of their workforce. On-the-job training is an important tool for this purpose. Following a design science research approach, we present in this paper a methodology for transforming business process activities into simulation based serious games that can be embedded in real ERP software and used for effective on-the-job training. In order to create a verisimilar environment for the learners, the key principle in our methodology is the encapsulation of the training activity inside a sub-process where all the relevant aspects of the process can be simulated and controlled without impacting the overall business process. Implementing this approach in our own simulation software integrated to the Odoo ERP software enabled us to use this training approach in a very effective way.