There is a multiple thing that can be added : 
1. Put the key to his cage on the ground with a magnet on it.
2. To get it it will force the boy to lower itself (the attachment on his wrist will allow him to slide. By sliding down the boy will be forced to get to on his knee. 
3. On the ground add a dildo to ensure the lowering kept the boy occupied ;-)
4. As soon as the boy get the key attaches to his lock he is allowed to detach his feet and hand attachment
5. As soon as it is done the boy will realize that the key is not for his chastity but for something else (like a pizza or to open the door to the next step ;-))