Insert the Mac OS X Install DVD (for OS X 10.6 Snow Leopard).
Double-click on Optional Installs to open the folder.
...
Alternatively, run the standard installer, but under "Customize" uncheck everything except Additional Fonts. (Couldn't test this, because the optical drive on my Snow Leopard machine no longer works, and I can't get CD/DVD sharing from my Yosemite machine to work.)
Someday, I'll learn.
I'm pretty sure that I must have looked in that folder (or...maybe only its previous incarnation in a pre-Snowy installer) at least once, and I had long since forgotten that it exists; it's one of those things that I don't even se when it's on the screen in front of me.
You can't turn the trick with the standard installer, because "Essential System Software" can't be unchecked.
Edit: Pacifist is beneficial to those who closely manage their fonts, because it's the only way to specify which of the additional fonts you want installed.
