Secret contracts, covert real-estate deals, scurrying around after nightfall to avoid detection: this is how far big-bank brokers are prepared to go when they plan to go independent. The Botkin Group, a team of brokers in Pittsburgh who produced $1.6 million in revenue last year for Morgan Stanley, went so far as to require non-disclosure agreements from contractors who made new signs, installed phones and delivered furniture to their new office. “We felt like we worked for the CIA,” said Lester H. Botkin, 35, the youngest of the group, which also includes his father, Lester P.