Is there no way to cheese the seasons changing?

I really love munchlax and I wanted to get one in Pokemon Black or Black 2, but the in-game trade for one in BW is summer only and it felt a bit silly to wait all the way until real life july for it (which if i'm not wrong is the next time it will be summer in-game) I tried on 2 separate systems to change the clock but the game is still in autumn, did they make it so you can't cheese it?