Actually Mik you just provoked an interesting thought - the water system isn't under very much pressure, is it? What could possibly be a drawback to doing exactly as you said - replacing a section of the hard piping with appropriate rubber piping, which would allow some flex and easy fitting of the banjo bolt onto the turbo? Surly if you routed it correctly and insulated appropriately, the heat from being near the manifold etc would be negligible. Especially if you positioned this rubber piping further towards the back of the block, away from everything.