"Why don't you just pay all three and send the other two away?" Yossarian suggested.
"Because then mine will be angry with me for making her work for her money," Nately replied with an anxious look at his girl, who was glowering at him restlessly and starting to mutter. "She says that if I really liked her I'd send her away and go to bed with one of the others."
-- Catch-22 by Joseph Heller
Why not simply not pay the other two? Won't they then leave and try to find a guy who'll pay them to go to bed? If his girl threatens to leave with them, he can offer to pay her double or even triple; that shouldn't be a problem since he had lured all three there with promises of $30 each - which occurred pre-excerpt. She gets all $90 for $30 of work, and the other girls get nada.