If a Pokemon with Hustle, Pressure, or Vital Spirit is leading the party, the chance of encountering a higher-leveled wild Pokémon increase by 50%. Unfortunately, you cannot have a fainted Pokemon leading the party to get the effects of these abilities because of the Nuzlocke, so it only works of one of the Pokemon you're grinding has the ability. Also, you can try to use the Repel Trick and combining it with a White Flute, but again, this only works if you have a fainted low-level Pokemon leading your party. There are ways to do it in these games, but not with Nuzlocke.