So last night I decided to make it into a cardigan because cardigans are the greatest things in the world and because it would give it a cooling factor for indoor situations.
Sorry I didn't take photos (it was evening), but all I basically did was rip back the collar (which was folded and tacked down) to about 6 rounds and bound it off again. Then I found the centre column of stitches on the front, ensuring it was in the middle of the yoke motifs. This happened to correspond to the decrease rounds in the yoke, so it was not so much a strict column of stitches up there as a vertical line. Then I took some slippery superwash sock yarn and my big needle and stitched a quick line where the middle is.
Then I took out the sock yarn and cut straight up the middle. Picked up stitches along each side and did 6 rows of seed stitch like the cuffs and collar, buttonholes on one side. Added buttons. Tacked down steek sts to the inside. Et voila!
I am going to wear this a lot more now.