This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
I don't know that James has a Java API for that. You could analyze the code that's run if you add users interactively; it probably just creates a few files (or DB) entries that should be easy to create in your code.