Pfft yeah. We can put their levels to 100, so that their HP will be as high as it could go, but only use the moves that the Pokémon knows now. For instance, Gible only knows Take-Down, Tackle, Sand-Attack, and Dragon Rage. Nidoran knows Leer, Peck, Double Kick, and Focus Energy.
Edit: Hm...but Gray has two Pokémon, and I doubt that he'd lose both to your Riolu. xD No offense.