The technique I use is a bit hard to explain, but the jist of it is to push down both the + and - keys simultaneously. With my left hand, I put my ring finger on the - key and my middle finger on the + key, and since my ring finger carries more weight (this may be different from player to player), I also remapped the buttons and swapped them so + is being pressed first each time instead of -. Then it's just a matter of vibrating my hand until Route 2 is done. I explain this more in my Beat Brock Guide which you can find here: https://www.speedrun.com/pokeclicker/guides/m64gm