New York--Interpublic Group's Western Trading L.L.C., New York, launched Tuesday eAdvantage, a program that allows Internet start-ups to build brand awareness without breaking the bank. In exchange, Western Trading gets an equity stake in the new venture. The program goes to market with a client already in tow: MortgageIT.com. Although many advertising agencies and public relations firms trade services for equity, Western Trading says eAdvantage clients will get opportunities to grab last-minute prime advertising when it comes open. Firms have been reluctant to offer prime placements to new customers for fear of alienating long-standing ones.