In a recent Rails app I was working on I came across this problem, luckily everywhere we had this problem was in content being rendered using the simple_format text helper. So with a little bit of research (thanks John Resig and Stackoverflow.com) I came up with this simple solution:

There one serious caveat to using this, it will cause problems if you allow any html or other markup in your comment (we do not).

There is also a javascript solution to this problem which may be more suited to you, Hyphenator.