Bluetooth SPP - BREAK Support
Looking at the RN-42 Advanced User Manual the only mention of a hardware break appears to be on page 20 for the SB set break command. That only sends a break to the local serial port but you may be able to use the remote configuration to send the set break command from the PC end of things. That won't be transparent however so you'll need codes changes to the PC application.

I couldn't find any references to how Bluetooth SPP (Serial Port Profile) devices should handle hardware breaks although it not getting passed through wouldn't really surprise me. Many legacy devices used the hardware break in different ways and I believe most Hayes style PSTN modems wouldn't pass it through either.

Because you're using a microcontroller personally I'd make my own escape sequence to indicate that the break should be set for a certain period. That way it will remain portable if you ever want to change Bluetooth transceivers at either end.