I had an hour yesterday and another one today on the train and I wrote a small plugins to make gmpc integrate in the ubuntu SoundMenu.
There is a small bug in SoundMenu not showing the complete name, I reported today and is fixed upstream (https://bugs.launchpad.net/bugs/744142).
You can get a trail version here: http://download.sarine.nl/gmpc-appindicator-0.0.95.tar.gz.
I am going to need somebody to finish and maintain this code, so if you feel like this let me know. Most code is already there and it is not a lot.