The only way that I have found to turn off justification is to embed
the Bookerly font using Calibre with a left margin.
Not exact matches
I'm actually
using the
Bookerly font on the KK and it looks really good.
Bookerly was developed last year and many of the Kindle devices and apps
use it as the default
font.
At virtually any size (it's easy to change
font - sizes on the Kindle
using the familiar pinch to zoom motion),
Bookerly is one of the most readable
fonts I've ever encountered.