I haven't done this since like 2001, since I got some huge time off thanks to a post-release lull. That was a good week, I spent one night making food/leftovers for the whole week, and then geeked out and played through like three games, though the only one I can remember was Summoner 2.
I'd say that you need to find a game that you can just catass the fuck out of. I'm talking serious ass-bruising, indent-your chair or couch insanity. If you get up to do anything but evacuate waste or get booze and food, YOU FAIL.
My choice would probably be Titan Quest, or a deep management/strategy game ala GalCiv2/Dominions 3/good, objective/scenario-based city-builder.
I couldn't do it with Oblivion, too much about that game pisses me off to keep going.
Edit: Also, a console RPG isn't a terrible thought.