Not trying to be snarky, but why not use something like Thunderbird (or whatever comes default on the OS of the machine that you're using) that will render out the HTML natively?
If he's anything like me, a fellow mutt user, he cares more about speed and the text itself than pretty columns. It's surprising how little you miss html, particularly when breezing through email at a rate of knots. Plus system resources. So many resources.
