I just stumbled over an older experiment of mine that I somehow forgot to publish: it’s a tiny component that allows to render fully justified dynamic textfields. Here is a demo that shows how it behaves - you can drag the lower right corner to resize the textfield:

As usual with my experiments, there’s no documentation, but I hope that if you take a look at the FLA it shouldn’t be too difficult to grasp how it works. Download QM_fullJustifiedText.fla here.

UPDATE: I just uploaded version 1.1 which has a “snap to pixels” option in order to render pixel fonts properly