The baseball season is a week away, bringing with it pitchmen as well as pitches. FleetBoston Financial may consider bringing back two of its favorites: New York Yankees shortstop Derek Jeter and Boston Red Sox shortstop Nomar Garciaparra. The Fleet Homelink ads in which the rival shortstops appeared last season drove in twice as many customers to Fleet's online banking program. During the ad campaign the rate of online enrollment spiked from 50,000 to 100,000 per month, reportedly more than doubling the number of customers to a current 3 million. "They are excellent role models," said Rena DeSisto, senior v.p. of corporate marketing and communications, and confessed Yankees fan. Nomar's better.