Ooops, I have not publiced my latest instructions!
I had the same problems as Balbuze. But I is possible to install rpi-gpio without killing Volumio!
wget http://sourceforge.net/projects/raspberry-gpio-python/files/raspbian-wheezy/python-rpi.gpio_0.5.8-1_armhf.deb
sudo dpkg -i python-rpi.gpio_0.5.8-1_armhf.deb…and this works
Succes!
Harry