I have known of a couple of cases, but it is very unlikely to work for most people.
In one case, the person was gambling before and after baptism. They pleaded the case that they had not been baptised with the correct understanding, and got baptised again.
The second one was a person with mental illness that was engaged in wrongdoing before and after baptism. It was decided that due to her circumstances the baptism had never been valid and they just let her leave.
I unsuccessfully tried the get an annulment. The results are here http://jwfacts.com/watchtower/experiences/grundy.php.