I have tried coercion on the kitteh, as in:
" I WILL NOT PLAY BALL UNTIL YOU DROP A JEWEL!"
I have tried sneaking up behind them wearing a dog mask
and shouting ' WOOF!'.
I have tried giving them 'mineral' water. . . .but still nothing.
A cat will drop a jewel only when it wants to and on ITS terms.
Good luck with that!