ah, I assumed there was one already. I somehow doubt we can add one.
What about if it was something like if you held the space bar as you folded it back it knew to go into tablet mode?
A bit of a hack, but so is the blinking for function lock feature.
edit - actually, thinking about it, that may cause extra spaces to be entered in whatever you happen to be doing, it might make more sense to say "if the space bar is pressed within a few seconds after the hall sensor is triggered, go to tablet mode". (would require a few second delay before switching the screen off when closing it though.