Two things come to mind.
Buy a crate and let his owners pay for it upon their return.
Take him to a boarding kennel and let his owners pay for it upon their return.
The latter is likely to cost more, and along with some explanation from you, may trigger them into responsible dog management. May not.
Minimally, they deserve to get a phone call from you.
Bottom line, I certainly would not give the pup a chance to destroy your property and risk harming himself in your laundry room, so a crate would have been bought yesterday if I were in this position.
If you think about it, because of the lack of boundary teaching with this young buck, these people have put you into quite a position. If the dog hurts himself because he is a wildass indian, will they blame YOU upon their return?