Hmm...yes, that version has the support for button C. Just to clarify the steps should be:
1) Open NameBoardSketch, change the variable name from "ARDUINO" to the name of your sketch e.g. "BLINK".
2) Format the SD with FAT16 and place BLINK.HEX in the root folder.
3) Power-up the Gamebuino holding the C button down.
That should cause BLINK.HEX to be flashed into the Gamebuino and then executed. It should work without a reboot but if it doesn't then try a reboot anyway. It's late in this part of the world so I'll have to leave this until tomorrow, the next version I upload will also output a debug stream to the serial port so we can figure out where it's failure.
Sorry it's not there yet but hey, at least the USB part is working