I don't think you can do that inside your graph, maybe we should code your app to display them next to graph. Pros: labels get indexed by search engines.
I need a tiny fix: the set-radius methods are not working as expected: they set the radios from the center of the unit/value. But if my value/unit name is long (e.g. 10 - 15 chars), its first letter is to close to graph. The radius should be computed from graph center to closest character from unit/value text.