What Jazzcat said - clean EVERYTHING needed with an enzyme cleaner to get rid of the pee smell. That helps the humans, but also the cat doesn't get a 'scent' message saying it's ok to pee in that place.

Cat Attract litter - if that is too expensive, there is something you can add to the litter to make it smell attractive. ALSO, try an extra litter box.

From a post by Jen Luckenbach:
cat attract litter IS quite expensive, but I found some places offer it cheaper than others.

Also, there is a product to add to regular UNSCENTED litter. http://www.preciouscat.com/attract-l...-your-p-7.html

http://www.healthypets.com/catattract.html

http://www.amazon.com/Dr-Elseys-Prec.../dp/B000IJ9MCU
I think he is just upset because he doesn't like being alone. They could get him a cat for a friend! If they try the Feliway, have them spray a tiny bit on a stretchy collar. It lasts way longer and is "with" the cat longer.

Another option - rehome him with people who will be at home more often. That is drastic - but not as drastic as PTS.