I can't be the first person that's converted a cantilever or V-brake bike to disc brakes and looked at those empty brake studs and thought, "wow, that would be a slick mount for a fender!"
My current commuter has no eyelets for fenders front or rear so I'm using SKS Raceblades with extra long mud flaps. They do an adequate job of keeping me (and the folks behind me) clean & dry but my frame and drivetrain get super grimy after each rainy ride--which in Seattle has been almost every one since last October!
For next year, I've got a Redline Monocog 29er sporting 700x40 cyclocross tires and disc brakes which should be a nice rig for my daily 20 mile roundtrip, but the fender situation has me perplexed. I can make a front fender work by using a different fork, but I kept looking at those empty brake studs on the back and thinking that maybe I could cut & bend the fender stays ... which would have the added benefit of keeping them out of the way of the disc brake.
Before I proceed, though I thought I was see if anyone has already tried this? I figure I've got at least 6 weeks of sunny weather to get this figured out before the rain returns...