There is currently on explicit support for file transfers. File transfers rely on a protocol called Object Exchange Protocol (OBEX), which is a high level protocol. This is required, so the devices can understand eachother on a higher level than the supported low level protocols.
The protocol stack looks like this (simplified):
OBEX File Transfer (Agreement on how to respond to packages)
OBEX (Protocol for sending get/put packages)
RFCOMM (Binary connection)
So OBEX File Transfer relies on OBEX. OBEX is currently not supported, but RFCOMM is. Therefore, you can look at the OBEX specification available at http://www.irda.org
to implement OBEX communication. You can then look at http://www.bluetooth.org
to find out which packets to send to initiate a file transfer.