The day after figuring out how to extend the Graph class to represent mixed graphs, I realized that I don't really need mixed graphs; all I need is to draw them as if they were mixed. I achieved this by writing a Predicate to check for the existence of a return edge, and another to match only the ascending edge of two-way pairs. The result is what you see here:
This mockup is still far from finished, but it should give you some idea of how gorgeous the map will be. I love how even the one-ways in are included in the distance filter; Prefuse took care of that detail automatically. The final version will convey a lot more information through colors and icons, and of course it'll have a nice starry background and look totally awesome.