Wouldn't this mean that the twiddler would have to send two HID codes for two different keyboard buttons at the same time?
You can probably send them one after another, if you add another "keyboard" line for the shortcut, maybe with a delay in between. And you may have to use the keycode 225 (0xE1) if you only want to send the left shift keyboard button, for example.
Or could this be a case for the "direct key mode"? Never tried it so far.