The 2 options are valid.
Either use the a separate LLBLGen Project for the membership functionality. And if you need relations with yourbusiness entities, you will have to remap them in the other business specific LLBLGen project.
Or use a startup template LLBLGen project which contains the membership entities, which you use to start any new project, and this way you will have these entities integrated with your application entities, as youwill need some relations between the application domain entities and the membership entities.