This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates 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.