I'm sure this is not a recommend fix, but I was able a new font to a JavaScript file. I'm sure this change will be lost on the next upgrade. But if you really need that font, you can add it here:
C:\Program Files (x86)\SmarterTools\SmarterMail\MRS\Common\Controls\ckeditor\ckeditor.js
Just search for "comic" and you'll find the list of fonts. Be sure to make a copy of this file before editing it.
Matt Lyons