He said he thinks he should pay more taxes, and that he currently pays a lower rate than his secretary. Period. He's not weaseling out of anything. The only people trying to weasel out of it are the ones saying "he didn't specifically say dividend taxes."
But he doesn't need to get the law changed, or get our permission, to pay more. He wouldn't be the first to donate something to our government or nation if he just sat down and wrote out a check he thought would be his greater responsibility.
Talk like this is poker chitchat. Count the cards and do your own thinking.