1. buy a Chinese cable, that is thin enough so that it goes along with the HDMI cable in the back.
2. Open up your original cables housing that connects to the 360, that will make it thin enough to go along with the HDMI cable.
3. Get an audio adapter specially made for that purpose. these are thin enough to go in along with the HDMI on the back.
here is the PIC, i saw it at faridabad's croma, so must be available at other cromas as well