I don't think the owner has done anything yet.
The simplest and cheapest thing by far, would be a trapout/extermination combination. I know someone else who did something similar, so this is what I recommended the homeowner do:
Buy a bug-zapper that will fit along or as close to the entrance that the bees use. Mount it and leave it on 24/7 for three or four weeks. As more and more foragers go out and don't come back, brood will emerge and stores will be used up - solving the potential "drippy mess" problem. Eventually a starve-out or abscond will result (not that they'd make it very far if they absconded). He might have to reposition the zapper a couple times for maximum effectiveness.
Once no more bees are going to and from the location, the owner can get up there himself and remove the tiles, check out the damage, remove the combs if he can reach them, clean the area with Pinesol and seal it up really well.
That was my advice. I am by far not the most shrewd when it comes to business wheeling and dealing. :sigh:
Good personal karma, I hope. Still wish I could have those bees.