You can disagree with Kenny on two major decisions other than the one when he asks you to kill Larry. If you fail to meet those requirements he will question whether he should help you or not. If you tell him that you need him, he'll say that you've been looking out for yourself and that he's been 'keeping score' even if we haven't.
However, he will tell you that he'll wait for you until you come back, or at least until nightfall, and that he'll take you even bit. In my opinion, that's the best option in hindsight, considering it's ideal to have someone guarding and ready to go with the boat.
But if you fail too meet those requirements and instead say that clem is your family, he may come with you depending on how you treated Katjaa & Duck. I'm not sure what the variables are here, but I would assume the Shawn or Duck decision and siding with Kenny or Larry in the drugstore on the topic of whether he's bit or not are influences.
And finally, you can tell Kenny to go fuck himself, which I was very tempted to do at that point. He won't come with you, and he doesn't mention anything about waiting for you with the boat, so I don't think this is a good idea...