Hi Alex,
this is currently not supported. The problem is that each scenario is implemented as a separate class and therefore @BeforeClass / @AfterClass does the same as a normal @Before and @After. I have thought about this problem before, but haven't found a simple way to add this feature. Furthermore, in my experience the use cases where you need a Before/After class are not that common. Much more common are cases in which you need to setup something before all the tests are run, which looks like your use case. These can be easily solved in other ways...
Feel free to disagree, ;-)
Sebastian