There is no simple way to do this (unfortunatly). However, I did find out a way a few years ago. It involves I believe write protecting a certain history file in the preferences folder so that Safari can no longer write to it, thus not being able to keep track of history.
No idea if this would work, but off the top of my head, if the file that Safari uses as it's history were removed and then a symlink to /dev/null was put in it's place anything it tried to write to that file would just end up being nuked. Of course, if one were to try this and their computer killed a bunch of people in the process, well if you try this, you're on your own.
Like I said, not hard to do, but it should have been an option in preferences anyhow. The main reason I wanted to turn the history off is because Safari will always try to autocomplete the address as you type it in. My parents type very very slowly, and they found it confusing to type in a letter or two and have like 20 websites pop up and autocomplete in.