you did the first option that I was going to suggest - but sometimes that only helps a little bit.

I just double checked the IE 6 Tools/internet options {i didn't upgrade to IE7 because I don't use it much} and it doesn't have a setting to force the webpages to use your font of choice.
The Mozilla Firefox browser does have a option like that, but I haven't used it yet.

But you might try setting the font to a different style and it might have wider spacing or just better readability.
I don't remember what the generic one is but I changed mine to verdana and lucida console- those seem to be easier for me to read.

another option is to get him some cheap reading glasses that stay right at the computer.
vision clinics also do have specific glasses for computer use- because the distance is a bit farther than normal book reading distances.
hope that helps