@ArcadEd, thanks for the effort!
I am quite aware of the issue, but currently I don't see a way to tackle it. So I'm afraid to say that SpriteFont doesn't really play nice with CocoonJS.
A rewrite is pending, basically a slimmed-down fork of SpriteFont (no backwards compatibility). Right now, however, I am swamped in projects, so it may take some time.