I like #2 very much, but I would place a pair of lit candles, perhaps an inch and a half in diameter, just beneath the lovely slave's pendant pleasure-globes. She has been ordered not to change her position but the golden flames of the candles will strain upward to lick at her breasts. The reach of the flickering tapers will fall just short of their delectable targets, but even so, the heat the candles give off will be cumulative, and can only be ended by snuffing them out with a quick decisive dip of her breasts that will smother the wicks in the hot wax.
Her master and his friends place bets on how long the lovely slave can resist the heat of the flames before summoning up enough courage to end the torment by plunging her breasts into the wax....