Toys R Us is prepping for the upcoming holiday season with plans to open 600 temporary or "pop-up" stores. Last year, it had 90 temporary express stores in operation -- largely in retail-center space once occupied by KB Toys. "We did it last year and it worked," CEO Gerald Storch said. The concept of temporary stores is gaining traction. "It helps fill vacant space, so landlords can gain revenue when they otherwise wouldn't, and retailers can test certain concepts," said Jesse Tron, spokesman for the International Council of Shopping Centers. "It's a nice fit for both."