When comes to creating desire for the reward object there are only two approaches. The first is to make use of a young dog’s desire to play and the second is to train the dog to engage the reward object. Play is much easier to use and develop. Using food motivation or negative reinforcement to engage with the reward can work, but have limitations.
When thinking about play, here is an excerpt from the seminal work on animal play The Genesis of Animal Play by Gordon M Burghardt.
BURGHARDT’S FIVE CRITERIA FOR PLAY
1- Play is not fully functional in the form or context in which it is expressed.
2- Play is spontaneous, voluntary, and/or pleasurable, and is likely done for its own sake.
3- Play is incomplete, exaggerated, or precocious.
4- Play is repeated but not in exactly the same way every time, as are more serious behaviors.
5- Play is initiated when animals are well fed, healthy, and free from acute or chronic stressors.