Recently, it has been noted that the inefficiencies in peer-to-peer (P2P) overlay networks result in a large quantity of traffic among internet service providers (ISPs) or autonomous systems (ASes). To optimize cross-ISP/AS traffic, the existing approaches introduce network-aware strategies in which peers select geographically close peers as neighbors using topological information. However, each P2P application must be equipped with a locality-aware neighbor-selection procedure and/or a communication protocol to obtain the topological information from an "oracle" server, i.e., modifications of P2P applications are required for this scheme. In this study, we propose a novel approach for P2P traffic localization, called P2P-DISTO, featuring the insertion of an additional delay into each P2P packet based on the geographic location of its destination. Because P2P-DISTO is implemented on network routers independently of applications, it can be utilized by all P2P applications without software modifications. The experimental evaluations using existing P2P video streaming services show that our fundamental concept successfully achieves P2P traffic localization by discouraging connections with faraway peers due to the additional delay.