The legs on the pic you posted look like a single chunk of a feather. If you snip the tip of a feather off and look at what's left, you'll see what I'm talking about.

Snip again down below and use the resulting chunk for your one-piece legs.

You'll want a wee bit of the stem left on each end to make it easier to tie it in.

That's what it looks like to me anyways. Much easier than wrapping hackle, just pull the barbules straight out to the side, snip the end, snip a few barbules along the stem from each end...

After you've tied on the abdomen, tie the wing case (pointing towards the barb end), tie in the stem that was the top of the feather onto the thorax area (with the feather pointed back) then tie the thorax, fold the feather chunk forward to create the legs, tie off the end near the hook's eye, fold the wing case foward, tie it off...

If that's not clear, let me know and I'll try again (and see if maybe I can create a picture or two during the holiday break).