When I replaced my steering rack, I noticed that the bottle is accessible when you remove the plastic liner of the O/S wing. That looks like the way to go - it's not difficult. Take the wheel off, there're a couple of screws to undo, right under and at the front of the wing, and a couple of those hollow nylon rivets with a plastic drawing-pin like object pushed into them. Lever out the drawing-pin thing, and the plastic rivet comes out. There's a name for these, but I've forgotten it.
