Here I used an i-cord tab cast on of 4 rows, then picked up 3 stitches in the center for a total of 9 stitches on the needle. Worked following the Sheep Wagon Shawl pattern instructions on the 3 center stitches with the addition of the 3 i-cord stitches on each side. (I-cord: Knit 3 at beginning of row; sl3wyif at the end of each row.)
Joined to work in the round after row 57. Yes, this pattern requires a lot of purling while working flat (have to purl every return row), but that's the price you pay for wanting a design in classic, classy stockinette. Once you join to work in the round, however, you're on all-knitting easy street.
Update 5/14/15: I started out knitting this poncho with size 9 needles (5.5 mm), but the fabric was just turning out to be way too dense. So somewhere around row 70, I ripped the whole thing back and started over with size 10 needles. Painful to lose that much work, but I'm much happier with the fabric the second time around.