Most bouncy balls that I've run across

>! can _float on water_. Thus, if it has rained recently, he could find a puddle nearby, and scoop handfuls of water into the hole. Since the hole's so small, it would only take a dozen or so handfuls to float the ball to the top.

Alternatively,

>! He could grab a somewhat flexible stick, and pound it with a rock until it _**split** at the end_. Depending on the nature of the surface of the ball, he could put the stick in the hole and wedge the ball into the split.