You can try to add: title="your text here" :in the style of your button
Hint-text on a button sounds like adding a title attribute to each of the button's dom elements. This, by default, will give you hover-over text.
If you go that route, you'd need to build a custom widget where you can dynamically point to a dom by id or class. Then edit the title attribute of the node.
All in all though, this seems like too much work just for some hover text. I would consider redesigning (showing labels on buttons, etc.).
I'm not using beta, but hopefully they add the title attribute to the common features of buttons.