I had to gave up finishing my Myrtle due to new discoveries about her uniform (under the robe) and the cost of the fabric so am borrowing a friend's (Simplified) Ringwraith Costume and coming as Dementor instead (well, someone got to become one).
For the hands, I'll attempt to paint a Blue Rubber Gloves with White Krylon's Primer and allow it to peel off here and there. If that fails, then it's to White Nippon Prylox (I know it kinda rubber base). Maybe add some long, anyhow cut nails too?
Anyway, have u check out the "Dementors" pictures? IMHO it was doctored (it look so much like taken from a picture of the Ringwraiths at Weathertop) but it can offer some tips.