Here's a bit of code I've been using myself for a few months now. It allows you to load in custom typefaces into your prototypes with very little effort. There is some basic error checking and testing to validate the typeface was loaded.
Here's how simple it is to add to your prototypes:
gotham = new FontFace name: "Gotham" file: "Gotham.ttf"
Check out the demo above or you can grab just the module if you'd like.