Bringing this back up real quick: I actually ended up doing this! I wrote a little less than 80 pages (by far the longest thing I've ever written for anything ever) in three days. It was really frustrating and spine-crushing but also incredibly satisfying. If any of you has a story you keep not being able to find the time to work on, I really recommend this - it's a great kick in the ass, and if you finish, you finish with a manuscript, no matter how rough.
Good times, as the kids say.