I think I missed the point here: What are these other techniques? I understand there is no good reference for the WB in the picture since even the white surfaces are reflecting the sky colors.
What happens if you pick the back of the boat, pointing towards you, near the door, as a reference for the WB picker? It seems to not reflect colored light from the sky but more grayish light from the other side.
Also other software can do nothing but guessing. Probably there is no “correct” WB here anyways. It is more about the mood that you want to see captured in the picture.