How do I reach the extra switches in the Waterway puzzle?
So, if you've hit the 4 buttons you've mentioned, and battled Riku, than there isn't any more buttons you need to hit in the dungeon. I can't specifically remember the buttons you are referring to, but in looking online, it seems you weren't the only one to notice them. But, they don't seem to be reachable, and they don't unlock anything anyway, so you can just forget about them. They are decoration.
Don't forget to get the other items in there though (notably a Blue Trinity and I believe 3 chests).