Multiple ghost instances

Continuing the discussion from Recommended Method to run multiple Ghost instances?:

If I am using the IP address of the server for one of the ghost blogs what am I to use for the IP address of the other? Is there a way to use a port of the IP?

I do have a domain name for this project, but want to build with the IP address as a temp domain per se.

In the end I want one ghost blog at a subdomain and the other at another sub domain. For example

Thank you!