Thank you for the suggestions everyone. I went with the flat shaded viewport capture using the grabviewport script. If anyone has any additional suggestions I'd love to hear them! This is what I have right now (the pose isn't ideal, but I can work on that later):
Really I'd just take high resolution screenshots rather than rendering them. Ravenslayer/Leslie Van Den Broeck has a script to grab screenshots at higher resolutions than your screen can handle: http://www.leslievdb.com That way, when you downscale them you get some nice anti-alliasing, but you're not having to fuck around…