Your Duemilanove can easily be turned into an ICSP (in-circuit serial programmer)...http://arduino.cc/en/Tutorial/ArduinoISP
Note: Missing from that site are instructions to disable autoreset. You must disable autoreset for Arduino ISP to work.
If I were in your shoes, I'd start with a bare processor (like an ATtiny85 or an ATmega328) and get the "Circuit (targeting an AVR on a breadboard)" working. From that point, you should be able to easily reprogram your BT without using the bootloader. Bear in mind that using an ISP restricts what you can do with the three ISP pins (MISO, MOSI, and CLK).