Please Note: Photos deleted in computer meltdown!
All my worrying over the shawl collar was for naught; it wasn't nearly as hard as I anticipated. Turns out the collar is easiest made if it grows out of a facing along the front edges into an extension, shown in the two pix above. The middle photo shows the extension on the needle as I knit it along with the armhole shaping. (Note that since I didn't start the facings when I started the body, I had to add them in. Not the optimal approach! That blue thread is the provisional cast on, which you may ignore.) The bottom photo shows the collar extension after the shoulder stitches from the front and back were seamed together. Top photo shows the collar after both fronts and extensions were knitted, shoulders seamed, and the collar extensions grafted together and sewn to the neckline. If I were to do it over, this is what I would do:
When casting on, cast on enough stitches for the body, PLUS 8 stitches on each front edge for the facings. On each RS row, I'd knit 7 stitches in st st, slip 1 stitch (to visually mark the turning edge) and knit in pattern to the last 8 stitches, slip 1 and knit the last 7 stitches in st st. This will form narrow facings that will turn to the inside at each front edge. When the body is knitted long enough to the underarms, the armholes get shaped and AT THE SAME TIME (dreaded words, no?) begin the collar like so:
Immediately increase the 7 facing stitches to 14 stitches needed for a full chevron repeat by knitting into the front and back of each stitch. If you do this when the pattern is on the first row of the chevron (only one yo) it will be easiest to incorporate. Then on every RS row, you want to increase the width of the collar while decreasing the front as for a V-neckline. Sounds complicated, but it's really not, as you can see from the photos. Put a stitch marker between the stitches that make up the facings and the stitches for the fronts; this is where you will increase for the collar and decrease for the front. On every other RS row (every 4th row, if you want to think of it that way) when you get to the marker, increase 1 stitch by picking up the bar between stitches, twisting it onto the left needle, then knit it. One stitch increased. Then move the marker one more stitch towards the front, effectively "assigning" one front stitch to the collar stitches. Two stitches increased for the collar, one decreased for the V-neck. Do this ever other RS row until you have only two full repeats of the chevron left on the fronts (don't forget you have also decreased armhole stitches.) As you can see from the pix, the shoulder seam is two chevrons wide. At this point, my collar was three chevrons wide.
The tricky part is keeping the collar stitches in pattern. As you increase collar stitches and "reassign" front stitches to the collar, those stitches need to be incorporated into the pattern started when you increased the facing from 7 st st stitches to 14 chevron stitches.
Once the armhole is the proper depth (9" for me) slope the shoulder with three short rows, then move the shoulder stitches to a holder and continue on the collar stitches only. Add one selvedge stitch to the shoulder side of the collar (so you can sew it down later) and begin the short row sections of the collar needed to give it enough fullness to fold over and lay properly.
Every other RS row (still every 4th row - I found it easiest to remember it was every 1st and 3rd pattern row) leave 6 stitches on each side unworked. I didn't worry about wrap-and-turn since that helps prevent holes, but since this is lace an odd hole at the edges of the shawl won't show. I did try not to leave any yo's unpurled, but even when that happened it doesn't appear to have made much difference in the end. Continue knitting the collar extensions until they reach just short of the center of the back neck. Then graft the two collar edges together (I used Kitchener stitch), and attach the edge to the back neck with a 3-needle bind off. Fold the collar in half and whip stitch the free edge to the bind off. I found I needed to pick up an extra stitch on each side of the back neck to keep it tight and tidy; just pick up a loose bar between stitches, twist onto the needle, and count as part of the bind off.
Once that's done, tack down the facing along the front neck and down the fronts by skimming the edge of the facing to the inside of the fronts. Ta da!