In my experience, people become much more involved in modeling when they have a visual frame of reference. Creating a diagram gives them something to react to. They can see everything that is being discussed, and they can immediately see the effects that their ideas have on the model.
Encourage participation in the modeling process. Never dominate the process. Use every question as an opportunity to get others involved in drawing and redrawing the model. People take to the process quickly when invited. If you consistently ask probing and specific questions using the diagrams as a frame of reference, then the participants will quickly build a working knowledge of the diagrams and become more comfortable offering opinions and ideas.

Managers and project leaders will gain an appreciation for the power and value of the modeling process as a means to solve many of the problems that plague the software development process. Hopefully, you will also come to appreciate the value of having a rigorous and testable tool to understand and solve a problem before committing to the expense and uncertainty of code. In short, I hope you come to see that the model is implemented in the code.