Based on what I've heard so far it seems like for 2008OS it will go something like:
1) Edit /etc/bluetooth/audio.conf and uncomment some line
2) Pair your headphones/stereo
3) Install Kagu
4) Launch Kagu and click its Bluetooth icon
5) Hit play and music comes out of your headphones/stereo

I don't know if it would be frowned upon or even be all that smart but it seems like someone could just make a package whose entire purpose was to update the configuration file in question. So that first step might be "install enable-a2dp.deb"

In 2008OS it should be much easier for applications to support A2DP, but it's not enabled by default.