How can you get a pretrial diversion for a first time misdemeanor?

Get yourself a private criminal defense attorney (try the Florida state bar, and/or www.attorneypages.com).  Make sure he or she has loads of experience with pretrial diversion programs for first time offenders.

Here is some information I found for you:

"Pretrial Diversion is a diversionary program run by the State Attorney's Office and is usually reserved for first time, nonviolent offenders. The diversion program is similar to probation, in that once you are accepted into the program you must report once a month to a supervising officer, undergo random drug testing, complete community service hours, and refrain from being involved in any criminal activity. Additionally, Pretrial Diversion requires the permission of the victim of the crime you are accused of committing. Your charges will be dropped upon successful completion of Pretrial Diversion".

Pre-Trial Diversion
When an individual (adult or juvenile) has been charged with a crime, the State Attorney screens the case to determine eligibility for the Pre-Trial Diversion Program. Eligibility is based on prior criminal history and the severity of the crime. If the individual is found appropriate and accepts the program, the case is abated until further notice from the State Attorney. Upon successful completion of the pretrial term, the case is dropped by the State Attorney's Office.