How can I disable Bluetooth A2DP profiles on the iPhone 4?

The app you are referring to has a manual process you can try, but it is not for the faint of heart: http://blog.ramondeklein.nl/?p=257

Howto disable A2DP on the iPhone

The interesting directory is /var/mobile/Library/Preferences, where the iPhone stores the BlueTooth settings. These settings are stored in the PLIST format, so you need a PLIST editor (Mac or PC) or you need to convert them by hand. Transfer the com.apple.MobileBluetooth.services.plist to your computer or you can use iFile to edit the file on your iPhone directly.

Open the com.apple.MobileBluetooth.services.plist in your PLIST editor and make sure you edit the A2DPService section and store the devices you don’t want to use A2DP in the UnauthorizeList (without the letter “d”). This dictionary will probably not exist yet, so you need to add it by hand. You need to know the MAC address, but it is probably listed already in this file.

<key>A2DPService</key>
<dict>
  <key>State</key>
  <true/>
  <key>UnauthorizeList</key>
  <dict>
    <key>00:10:60:D0:91:D0</key>        <!-- This is the MAC address -->
    <date>2009-08-08T01:00:00Z</date>   <!-- Timestamp -->
  </dict>
</dict>

Transfer the PLIST file back to your iPhone and reboot the device. Once it gets back on, then the A2DP service should be disabled.

Do you not just need to do this;

1. Connect via bluettooth
2. Go to the iPod app
3. Click on the hidden button bottom right that only appears when you are connected to Bluetooth.
4. Select the output device that isn't your handsfree destination, it seems to remember this choice on my setup(?)

That worked for me when I had the same problem