first you have to create the callflow with your game and your queue in different CFs. If you have done this, you might use modules to check, if agents are available or not. By checking the queue you can jump to the other cf. in the Game you have to build some asterisk check to check of agents are still busy or not. Then you can decide if the caller should continue gaming or should be forwarded to the queue.
Using this construct will not show "waiting" callers in the wallboard