It's been ages since I did this in OSX Server, but I distinctly recall adding an extra IP address to a single ethernet port just using the regular System Preferences>Network stuff, just like you would in OS X Client. This is described in detail in the QuickTime Streaming Server docs. The standard configuration is two IPs on one Ethernet port, you need a second IP address to run the QTSS server over port 80 while your main IP address serves HTTP on port 80.

So.. I don't see why you need to do this through the command line. If you must have a GUI for remotely adding it, use Apple Remote Desktop or VNC and just tunnel into your remote CPU's desktop.