I am not aware of any solution that is public and/or free. You might try contacting the devs at:
http://osticket.com/support/contact.php(http://osticket.com/support/contact.php)
Please note that this is a paid service. The last time I remember someone else asking this question was during the last major release (1.5).
Your best bet is to probably write a script to move the data from one DB to the other, but that's probably not for the feint of heart.
Good luck.