pwnat, pronounced "poe-nat", is a tool that allows any number of clients behind NATs to communicate with a derver behind a separate NAT with *no* port forwarding and *no* DMZ setup on any routers in order to directly communicate with each other. The server does not need to know anything about the clients trying to connect.
Log on to your N900.
Get and extract pwnat source:
wget http://samy.pl/pwnat/pwnat-0.3-beta.tgz tar -xzf pwnat-0.3-beta.tgz
Change c compiler in pwnat-0.3-beta/Makefile to gcc-4.2