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.
Is this what you're looking for? @Riddler