I fought him almost that many times and finally won by concentrating on just whacking the large bushes and the balloons, instead of running around trying to get lots of bushes. He runs faster than us. I don't know if that's the "secret" to winning or I just got lucky, but try that. Good luck!!
And BTW, you don't actually have to beat him to start playing BW2. The townspeople still show up there to help you. But it is nice to have that sense of completion and you get some prizes after you finish all that and get cloned.