At our university, we have a number of small-tomedium- size compute clusters and some technical simulations which could benefit from using several of these clusters simulaneously. To reach this goal, we discuss the formation of a "Mini-Grid" using a Virtual Private Network to couple clusters on the message-passing level. This is a simple and pragmatic approach for those cases where the functionality (and complexity) of full Grid middleware stacks is not strictly necessary. We evaluate the performance of our approach with a Cellular Automata Simulation using MPI. Experiments show that the use of a VPN offers sufficient communication performance for our application example.