We’ve been playing around with Axure, which also supports FontAwesome, and you can cut and paste the Unicode that FontAwesome uses for a character into a text area. Basically it’s a dingbat font that matches the icons used in the rest of the interface.
This is very useful for table cells with icons in them, or mixed-media areas like nav panels where you might have an icon in the middle of a sentence. You can replicate it with groups, but it’s much more fluent when it’s part of the text.
Balsamiq doesn’t have the ability to select the FontAwesome font for a control, let alone at the character level, so I’m not sure how this would work in Balsamiq–but consider this a feature request down the line.