I converted my mpguino to 3-wire, using the 74hc164. I haven't built an obduino32k, but i'll look at the code & see what I can do for you (and everyone else).
edit1: Ugh. It looks like all the LCD code is in the Arduino library, not directly in the obduino source. This may take a while. I'm surprised the Arduino folks didn't add a 3-wire option to the library code. It should be a popular option for people wanting to use extra lines for an SD card, or other inputs.
edit2: Looks like someone else already wrote a replacement LiquidCrystal library for Arduino, including your i2c. You should find all you need right here:
https://bitbucket.org/fmalpartida/ne...stal/wiki/Home