look for the pheasant tailed flymph in the faol fly of the week archive, its fairly near the top of the archive page, anyway it shows a good method for making soft hackles that you could apply the the flank feathers.
Parachute posts, steelhead collars, caddis antennea, zug bugs, traditional dry fly split wings for the flank feathers. If you have wing feathers, - no hackles, Caddis pupa wings, flying ant wing. Tons of uses...
McNeese' Black Duck Spey can be dressed with the black butt plummage found on a greenhead . Also wings on fan wing drys are to be had, and you'll also find some of the butt plummage has some sweet black/white feathers which may inspire you. This in addition to all the common soft hackles and spiders and spey wings you can dress from a mallard . cheers !
Tom Murray's Rolled Muddler uses mallard breast for the wing. This fly is more popular in BC than down here, but it's one of my favorite flies for searuns and resident coho. The pattern is readily available on several BC web sites - just do a search. I like a silver body with natural mallard wing, and a gold body with dyed gold mallard wing. Variations that I like are a cone head, red wool gills, and an olive marabou over-wing.
The Rolled Muddler is a very popular pattern up here as Tom has already pointed out. Here is the recipe:
Hook - Tmc 5262 0r 5263
Tail - Mallard flank
Body - Silver or gold mylar tinsel or opal mirage tinsel
Rib - Small or fine wire to match body, counter wrapped to protect tinse
Under flash - 3 strands pearl flashabou, doubled back and trimmed to length of taill
Under wing - Mallard flank
Over wing - Deer hair spun and clipped to form head leaving some deer hair tips extending over mallard
This is a photo of the bead head version. I just did 8 dozen for a shop up here in natural and olive size 8's for cutthroat. I do them in size 6's for coho (silvers)