[1.7.10] Multiple world providers

I am creating a mod that allows server admins to put a server into "Beta Test Mode." In beta test mode, each player can create his own dimension to fool around with. However, I've run into a small problem. How do I use the same world provider but have it generate different worlds? I'm assuming world providers are instantiated through reflection and I can't actually pass any arguments through to the constructor.

Another thing is I want these worlds to persist. When the server starts up, I want the world provider to continue generating the same world that was initially generate. (Kinda like how mystcraft does it.)