psientist's instructions are good, and a fairly useful way of saving different hosting parameters, but Applescript isn't required if you use the terminal in OS X.
The correct link to the command line options is:
Dominions X guides
The first guide in the list is the one you want.
Then you can simply cd to the folder with Dominions in it and launch the application with:
dominions2.app/Contents/MacOS/dominions2 --tcpserver
or whatever other flags you want to use from the above guide.
I do it this way because then Dominions uses my settings for DOM2_SAVE variable (which I set in my .profile file) and uses a a different folder than my home directory for keeping all the various saved files. There's probably an easy way to do this within Applescript too, but I don't know it.