Can I change employer during Opt Cap Gap Extension with an approved h1b petition from the current employer

Please advise if its possible to change employer before the H1B start date of Oct 1st,2014. I have an approved H1B petition from Employer A, and Employer B is willing to file a new petition. Is it safe to go ahead with this process? Will my current employer come to know if Employer B files for a cap exempt new petition ? Confused please advise.