Oxalic Acid is now approved for use. Beekeepers should treat in the most broodless time - which I estimate to be between Thanksgiving and MLK day in Mid January. See some nice resources including a video on the method here: http://adventuresinbeeland.com/2012/01/01/drizzling-oxalic-acid-on-bees/
Note in the UK they have been using this treatment for years and beekeeping supply stores sell oxalic treatment in that nice pre mixed container you see in the video. Here, Brushy Mountain sells a complete oxalic kit with everything you need and directions, as well as just the acid itself, or you can make your own from wood bleach.
See also Oxalic Acid FAQ