It's not possible today. There is no Bluetooth synchronization due to security reasons (Government is a major customer of BlackBerries, and Bluetooth is a significant security risk)
However, it's theoretically possible for a proprietary 3rd party program on a PC to communicate over Bluetooth to a proprietary 3rd party program running on a BlackBerry, using a proprietary synchronization protocol. So theoretically, synchronization could be emulated that way:
http://www.blackberryforums.com/viewtopic.php?t=4578
But a third party developer would have to take that responsibility, or that RIM itself would have to... (A 100% secure method of synchronization preferred.)