Instead, assign each remote device a globally unique IP in a separate address space (an overlay network) and translate between the overlay address and the local address at each site. The local device sees a packet from a neighbor on its own subnet and responds normally. The local IP address becomes an implementation detail. Protocols that embed IP addresses in their payload (RTSP includes the device's local IP in SDP) or use IP-based authentication may need testing. The local IP becomes an implementation detail, and the devices you need to reach get unique addresses that the rest of the network can route to without ambiguity.