The Double Feather Stitch can be adapted to smocking very easily, just as the regular Feather Stitch.

Follow the same instructions as for the Feather Stitch, but instead of entering and exiting the pleats 1/3 and 2/3 of the way down the pleating row, divide the row into fourths. That is, the first stitch lies in the top half of the row, the second 1/4 of the way down, and the third in the bottom half of the row. This way, three feather stitches instead of two lie between the pleating rows.