You can clone an entity by explicitly casting to IClonable and calling Clone(). This will return you a detatched entity with all of the fields copied. You should now call EntityManager.GenerateID() to assign it a new primary key and add it to the EntityManager. Make sure to assign the primary key before adding it to the EntityManager.
Here's an example:
Employee newEmployee = (Employee) ((ICloneable)employee).Clone();
mgr.GenerateId(newEmployee, Employee.PropertyMetadata.EmployeeID);
mgr.AddEntity(newEmployee);