Get a couple balls on a string so that there will be interaction with you/your pup and the ball. Though he's teething right now so tugging has to be gentle. I'd also play 'keep away' so his frustration to get it builds, making it higher value. Then you can add in the two ball game.
Hallmark K9 - Premium Dog Training Equipment - BALLS
If you do order, make sure you get a medium, not small(small size can be a choking hazard)