In this paper, we present a peer-to-peer (P2P) system with remote method invocations, combining RMIX and JXTA technologies, and underpinning the H2O distributed resource sharing platform. We show that the integration of RMIX and JXTA was possible due to extensibility of the former, which allowed to plug in the JXTA-based socket implementations. The result of this integration is a fully operational RMI implementation running on top of the JXTA P2P network, where methods can be invoked on remote objects located behind firewalls or NATs. We present results of tests showing that our implementation can be used to connect peers in different LANs that cannot interact directly, while in the case of direct connection the performance is comparable to that of RMI using standard sockets.