An attempt to map modifier key events to regular key up/key down events...

gistfile1.m

// FIXME: does not work as intended if both left and right modifier key are pressed simultaneously!!!

- (NSUInteger)modifierFlagMaskForKeyCode:(unsigned short)keyCode
{
  switch(keyCode)
  {
    case 54: // right cmd
    case 55: // left cmd
      return NSCommandKeyMask;

    case 56: // left shift
    case 60: // right shift
      return NSShiftKeyMask;

    case 57: // caps lock
      return NSAlphaShiftKeyMask;

    case 58: // left alt
    case 61: // right alt
      return NSAlternateKeyMask;

    case 59: // left ctrl
    case 62: // right ctrl
      return NSControlKeyMask;
  }
  return 0;
}

- (void)flagsChanged:(NSEvent *)event
{
  if([event modifierFlags] & [self modifierFlagMaskForKeyCode:[event keyCode]])
    NSLog(@"down: %u", (unsigned int)[event keyCode]);
  else
    NSLog(@"up:   %u", (unsigned int)[event keyCode]);
}