I've been doing multiline support the way that wiring does: not explicitly configuring it that way, but allowing you to move the cursor to any line you want. I can write to all the lines on the 2 and 4 line displays I have.
gradbert: The constructor for the LiquidCrystal library on Arduino will be basically what you suggest. The rest of the API will mirror Wiring's, although we could certainly add some functions (either now or later).