You could bind to "" and then check event.char and perform the action you want based on the value of that? Granted, I have no idea if this works when multiple keys are pressed at the same time, it may still run in to the exact same problem. I haven't used Tk in ages.
" The user pressed any key. The key is provided in the char member of the event object passed to the callback (this is an empty string for special keys)."