Despite the important role of simulation in the development and control of robotics systems, the majority of open source simulation tools has however paid no attention to the progress and paradigm change on the robot design in the past 15 years with the consideration of soft actuation technologies as a mean to power new robotic systems. More specifically, the integration of series elastic actuators (SEAs) into robots modifies significantly the dynamics characteristics of the system while the incorporation of the passive compliance into the actuators is not applied in conventional simulators. This paper introduces a scheme for the implementation of the SEA dynamics on a Gazebo-ROS framework exploited for the simulation of a new centaur-like robot. This approach is based on designing a custom control plugin embodying the passive compliance dynamics so that the controller associated with each joint receives both collocated and non-collocated feedback. A simulation comparison with Matlab validating the performance of the designed control plugin is demonstrated. In the end, a whole-body simulation of the centaur robot driven/controlled by the proposed plugin is presented.