In order to arrange heterogeneous simulation executions, it would be useful to have simulation tools that enable easy and fast creation of simulation sessions employing real-time software components beside simulation codes. Although there have been considerable amount of research activities in simulation community, the current simulation tools are not sufficiently capable to support such a cooperation between components working in real-time and simulation-time. In this paper, we propose a new approach for constructing hybrid simulations that leverages usage of simulation systems. We introduce HeteroSim, a Java-based simulation system that can execute discrete event simulations by employing both simulation and real world software entities. This model is applicable to many software related areas such as scenario-based software testing and development of simulators. As a case study, we are able to rely on this model in order to build simulations combining both the simulated elements of a High Performance Computing (HPC) system and already implemented elements of our Policy Based Management (PBM) framework, so-called POLICE [1],[2]. In this manner, it may be possible to study the efficiency of POLICE on management of HPC systems.