Some reports said you could slow the boss down 80% on first ball with Nanab berries and then its effect would be significantly smaller, but present. Not sure if to believe it without game master info, but if you're desperate, you can try.
I remember when it first came out and it was just a total nightmare how far it was. Then they brought it a bit closer after a few days and it was much easier to hit.
But hey, I know a trainer in my raid group that managed to let a shiny Kyogre escape because he couldn't hit ANY ball :)