Got the PCBs back & they worked perfectly (Brandon did the design, but gratifying to know that I'd remembered what wires went where!). See pics - you remove the big ugly board, replace it with this one (the mounting holes line up), plug the 3 cables in and insert an arduino. Very neat, uses existing power connector, the only component (besides the 0.1" headers) is a diode so you don't attempt to backpower the display from USB when you plug in to reprogram the arduino.
Here the bitmap is generated by an imp which is wired to the Arduino RXD pin, but you could generate it with anything and send over UART or USB. Gerber files & awful Arduino code to follow