Solution 1:

Got it. All you have to do is add multiple Ethernet interfaces in Network Preferences. And then just configure each one to the correct settings and you're set to go. I tested this by hosting two different websites on two different IPs by multihoming my iMac and it worked!

  • System Prefs -> Network dialog
  • Press the + button and select the interface you want to add to (you may need to go back and identify which one if you have multiple Ethernet ports).
  • Name the service and press "Create"
  • Configure the new service as you would a static (manual) interface
  • Click "Apply"