It feels a little kludgy, but I managed to get Hyphenator installed on this blog so the text can be justified.
I'm not sure if editing your template to add the
hyphenate class to the
post-body entry-content div is the only way to do it, but it worked for me. For some reason I already had my template under version control so it's pretty easy for me to add stuff to it even though I run into bugs in Blogger every time I try to update the template.
But I'll spare you the boring details of my complaints about Blogger.