You can bleed a loop using a T junction, with the middle bit coming off horizontally. You connect it up to a tap, so that water runs straight through and down the drain. This exerts suction on the middle tube. I don't think it's bleeding which is the problem personally, the radiator is very hot so it follows that it must have hot water inside it. If the radiator felt cool but it was overheating then sure, blame air stuck in the waterblock. Bubo is rarely wrong though.
I haven't taken a good look inside a 360, but it seems you may be missing an obvious solution. If you cut a large hole in the side, and mount a 120mm fan on it, it'll blow air into/draw it out of the case. If you also block off all the vents, the air must travel through the 2x40mm radiator. SS has a silent build on here operating on this principle.
Taken to extremes, if you mount fans everywhere you can blowing air into the case, and keep the only way out as through the radiator, you'll achieve airflow through the rad which eclipses the two fans currently on it. I'm suggesting blowing air inwards rather than out, as the motherboard probably wont like having hot air blown across it.
This would also do good things for noise, 140mm fans are a much better way to go than 40mm in that respect.
Time to drain 
