which methods of cast on's do you know?
Long tail is not the best cast on for lace.--its stretchy but not very, very stretchy.
a provisional cast on is a good choice, and then end with a knit on lace edge, (and pick up cast on edge for a matching lace edge.
you can also knit a lace edge, and pick up stitches (a reverse process!)
A LOOSE (use larger needle, and think about working loosely!) knit edge is pretty traditional for lace..
it really depends on the scarf and the first few rows of knitting--does the scarf have an edging (garter or sead or something?
or does it start on R1?
What cast on does the designer (or editor) make?
Are you designing it for your self? Swatch!