It happens every summer. The weather warms up, and sales at the online grocer Peapod go down, as much as 16 percent. It's not hard to figure out why. The company, based in Skokie, Illinois, does much of its business in the greater Chicago area, where the long, frigid winters keep residents inside, buying their groceries online. Come May, sun-starved Chicagoans rush outside and into neighborhood stores.

Peapod has tried to address the problem by concentrating its ad spending in the spring, experimenting with newspaper inserts and direct mail. The different tactics had two things in common: Each was directed to consumers at home, and neither did much to break the summer slump. So last spring, Peapod tried something different, targeting a new customer base: office workers. "What better place to tap them on the shoulder and say, 'Hey, what are you having for dinner tonight? Have you thought of having your groceries delivered at home?" asks Brad Porter, Peapod's regional marketing manager.

The Bureau of Labor Statistics reports that fully employed Americans now spend more than half of their waking hours at work--more time than they spend sleeping, recreating, or even kicking around the house. And as a consumer group, the fully employed possess staggering buying power. If you are a marketer seeking a lucrative and captive audience, look no further than the carpeted cubicle.

Of course, it's also an incredibly difficult market to reach. Employers, after all, want their workers to be working--not shopping. Still, a number of marketing firms are devising clever ways to scale the workplace walls. WorkPlace Print Media, the Mentor, Ohio, company that designed Peapod's campaign, is one of them. Forget about pop-up ads. The Peapod campaign consisted of paper discount coupons distributed to workers with their paychecks. The custom-printed ads were good for a $20 discount on a customer's first grocery delivery. Peapod spent $15,000 on 100,000 such coupons for an initial test campaign targeting workers at businesses throughout downtown Chicago.

The result: about 350 new customers. More important, Peapod cut its summer sales slump to 10 percent. "This is our lowest-cost print-media campaign," says Porter, "and it was probably 25 percent more effective."

WorkPlace Print Media's head of business development, Dan Wheeler, claims to have generated similar returns for other customers. Most of them are large marketers such as LensCrafters, Subway, and McDonald's, though a growing number of regional players are signing up. The company boasts a network of some 900,000 employers nationwide that have agreed to partner with WorkPlace by distributing its clients' coupons. A client such as Peapod picks the Zip codes it wants to target, and WorkPlace sends the coupons to the "host" business managers in those areas, who offer the coupons as perks to employees.

"In elevators, you have an extremely engaged audience. What else are they doing? You don't have a cell signal, you're not surfing the Web."

WorkPlace requires these partners to distribute those coupons to workers with exclusivity. The coupons cannot be left in an employee lounge or dropped inside a generic value pak, and there can be no other offer inside a worker's paycheck envelope. If a host employer uses direct deposit for payroll, the employer delivers the offers personally. "We love the program," says Brian Curin, vice president of marketing for Atlanta-based Raving Brands. The company operates nine franchised restaurants, including Moe's Southwest Grill, which ranked No. 11 on last year's Inc. 500. "Consumers who might not know we exist get this gift in their paycheck from their employer that says, 'Hey, you did a great job, so here is dinner on me over at Moe's.' We get faces that we haven't seen before."

Curin spent $12,000 on a WorkPlace Print Media campaign last spring to help expand Moe's catering division. Where the company's usual direct mail generates a 3.4 percent redemption rate, the in-office campaign sparked a 30 percent return, he says. After the campaign, the chain saw catering revenue jump 18 percent in some markets.

Paychecks aren't the only way to reach consumers at work. Captivate Network, based in Westford, Massachusetts, gets them in the elevator. The company broadcasts ads on 6,900 video monitors in elevators in 674 office buildings in North America. It isn't cheap. The typical customer pays as much as $77,000 a week to reach some two million viewers a day during a standard five-day workweek. "In elevators, you have an extremely engaged audience," says John Bigay, Captivate's vice president of marketing and programming. "What else are they doing? You don't have a cell signal, you're not surfing the Web, so the attentiveness factor versus other media is better."

Peapod's Porter is just as enthusiastic. He plans to run additional in-office programs in Washington, D.C., and perhaps Boston. And Curin is considering rolling out a campaign for all nine of Raving Brands' chains this year. "There are over 100 million employees in the private sector," says WorkPlace Media's Wheeler. "And we've only tapped 70 percent of them." There are tens of millions more lucrative at-work consumers to reach. That's a lot of coupons.