How can I connect to a remote machine?

My friend and I are trying to set up remote kernels.

He has a server at home running 1 kernel off of a Linux-based server. We're both on 8.0.

I manually set $RemoteCommand to

"ssh `3`@`1`-l `3` \"math -mathlink -linkmode Connect `4` -linkname \
`2` -subkernel -noinit >& /dev/null &\""`

and manually changed $RemoteUserName to the one he set up for me. The problem is, whenever we try and run the code, we get the following error message:

LaunchRemote::rsh: Command ssh [my username]@[his server address]-l [my username] "math -mathlink -linkmode Connect -linkprotocol TCPIP -linkname 51145@[my public IP address],51146@[my public IP address] -subkernel -noinit >& /dev/null &" may have failed (exit code 1).

The problem is, my public IP address is not the same as my private IP address, so I can't connect. How can I get Mathematica to recognize my private IP instead?