Well, after trying by myself for two hours yesterday my brother came over today and slipped it through in about 5 minutes, as usual.
Actually it was quite helpful to have two people. For the record, the way we got it in was to push the ATX-end through from the front - slide it between the frame and the radiator/fan at the point right where the tube (in its installed position) jumps above the frame rail on the drivers side. Then bend the flex hose and shove the bent part upwards between the fan and the engine as high as it will go. Now the two hard tubes are making an upside down V behind the fan. In that position, fish the ATX-end fitting between the engine and the frame on the drivers side so it goes out into the wheel well. Then pull that fitting towards the rear of the car as you lower the flex joint, sliding the entire hard tube through that space between the frame and the engine.
Sheesh. But at least I didn't have to dismantle the entire engine to get it done....
Next job is the power steering cooler lines