When I knit with ruffle yarn, I just knit in repeated short rows - think 4 or 5 stitches. Very easy. Pick up the first loops instead of casting on and away you go.
Or, there's the non-ruffle-yarn method, which results in a bit more spiral ruffle - big needles, thin yarn, cast on a whole mess of stitches (approx length of finished scarf), *knit a row, knit front & back of every stitch for a row (doubling your stitches)*, and repeat between the ** a couple of times, then knit a row to finish. Very easy, but takes rather longer.