Just reset the game.The game saves when it puts you in the hall of fame. I forget if it tells you exactly when it saves, but if developers names are scrolling along the screen it's safe to reset.

Per [Ivo Beckers' comment][1] it might not be safe to do this the first time since it's a bit different--but if you're just farming the elite four after winning once you can reset freely.


  [1]: https://gaming.stackexchange.com/questions/157224/can-you-skip-the-credits/157226?noredirect=1#comment328238_157226