I think it's a second nature for some people, B2, somewhere in life it was pounded into their heads that electricity is expensive.

At some point, I was told that it's more cost-effective to leave them on during short intervals of absence and I agree with you on that one. Maybe you could help Bob out with a little nudge, and offer to have $75k worth of new, bigger windows installed to save on electricity. Or, have skylights installed so he'll have a new hobby keeping them clean and sealed. Of course, you could always use battery-operated lights strategically located to foil him, buying dozens of batteries every month will definitely lower the electric bill. Also, it seems to me that if you can't cook or do laundry in the dark, then, well, you can't cook or do laundry anymore.

Oh! And don't forget, solar grids have been dropping in price for years!

If you have multiple switches for single lights, go to the least convenient one to him and set it to sit in the middle, the other switches won't work.