You can't expect the same performance from temporary employees that you get from full-time workers if you don't treat them the same way," says Joe Lethert Sr. of Performark Inc., in Bloomington, Minn. The marketing-services company, which had 1995 sales of $12 million, has 165 employees, and 20% of them are temporary. Not only does Performark offer its temps the same training as its other workers, but it also makes temps eligible for incentives and bonuses. For instance, everyone at Performark's 85-person call center competes for daily incentive prizes, such as movie tickets and pizza lunches. Temporary workers attend the six annual company outings, including the annual awards dinner-dance. The payoff for Lethert? He estimates that fully two-thirds of his full-time employees began as temporary staffers.