Volunteer computing is a relatively new computing paradigm that is often the only solution to large computational tasks. Due to the dynamic structure of the peer-to-peer systems that usually form the backbone of volunteer computing, obtaining accurate distance metrics using traditional techniques is infeasible. Thus, techniques that could improve system performance, such as dynamic load balancing, are very difficult to implement. In this paper, we show that the master-worker paradigm used by the overwhelming majority of volunteer computing applications results in certain network topology and protocol characteristics that render distance measurement method with zero network overhead feasible and preferable. Therefore, we present a simple distance measurement method that is based on passive monitoring of application-level traffic. We subsequently test the method using simulation as well as a reference implementation. The paper concludes by summarizing the strong points and limitations of the proposed method and proposing further research directions.