It might be possible for you to max out Bounce to 8 PP before taking on Morty. According to Serebii and GameFAQs, there are two PP Ups you can pick up now or soon with the help of the Dowsing Machine; one is outside the Pokéathlon Dome and the other is in Route 39. Supposedly there is also one somewhere in Mt. Mortar; I don't know if you can reach it without Surf. If not, you can also get a third PP Up from the Radio Tower's lottery; it's the prize if you have a pokémon with a trainer ID that matches the ones digit and tens digit of the selected number.