Think this is a repost, but interested in what you're planning. have you seen the arduino based fis control where the dude wrote 'Eduardo' to his fis display?
Are you going to open source it? There are a couple of open source kwp1281 libraries available, links here
http://nefariousmotorsports.com/forum/index.php?topic=7114.0title=I was looking at building one of the kwp1281 libs for Linux/android, but bit busy to spend a week hacking code atm