Here’s a trick that will allow you to use an oversized feather to form the collar on a small, soft hackle fly.
Begin by isolating the tip of the feather to leave a dozen or so fibers on either side of the stem. Then snip the tip off to form a triangular shaped tie-in anchor.
Start taking thread wraps down the hook shank. Place the feather against the hook so the tips on one side of the stem extend a full hook length past the back edge of the hook eye. Then make sure your thread is positioned at the location of the feather’s stem.
Now reorient the feather so its stem is parallel to the shank and anchor it, like so. Wrap the feather as you would a normal soft hackle collar, preen the fibers forward and bind them down to the hook shank. Again, the feather’s tips should extend a full hook length past the back edge of the hook eye. Then finish the body of the fly as normal.
Use any small hollow tube, such as the end of your bodkin, to push the fibers rearward and encircle the hook. While holding them back, take thread wraps behind the eye to keep them pushed back.