It's not quite as handy as a toolbar button, but you could add them to the Styles pulldown in the text sub-toolbar (or whatever you call that area above the ruler).
The process for getting something into that menu is not exactly obvious, though:
- Select a character in the desired style.
- Choose Styles -> Other
- In the resulting panel click back and forth (arrow buttons in the player(?!) controls) until you see your style (it will be "Raised" or "Lowered") in an annotation to the displayed character. [This the hidden voodoo. Probably a bug.]
- Click Add To Favorites and proceed from there.