Recruiting medical students for user studies is a challenging task. They usually have overflowing schedules and often limited experience using advanced prototype applications, which entails complex scheduling challenges and extended introduction and training periods. Among potential solutions to this challenge is the recruitment of engineering students to model of medical students' skills and knowledge. We believe that wider, more easily accessible pools of study subjects may effectively model more valid - albeit less available - subjects, particularly in early validation and testing studies in preparation for more detailed and mature on-the-field experiments. This is because, through careful and controlled transfer of knowledge and mental models, the gap between medical and engineering students can be effectively bridged. In this paper, we delve into some of the pros and cons of recruiting among the latter students rather than the former, and propose an approach based on estimating to what degree one can leverage engineering students as suitable mental models (ESAMMs). Additionally, we advocate for the need of a more systematic analysis and comparison of these two populations, especially in the context of XR for medical education.