There's nothing else within the editor that can be done that would result in a justified-centered combination. To be frank, I haven't even seen this in most text editing programs even from major corporations. Maybe it's possible in certain specially-coded systems that only allow centered text?
Beyond that, I'd have no further insight, and at this time it wouldn't be something the devs are considering for future email editor updates.
The only potential workaround I see being available for the phone, would be to get a screencap of how you want the text to look, then using that instead of the text. However, with mobile reformatting, this would potentially cause the text to look different anyway, since they'd be pre-set visually as an image, and unable to readjust sizing with the rest of the normal text.
... View more