Alrighty, this is what I did.
Use a needle 2 sizes smaller than what you used for the garment.
Start picking up stitches from the back neck (specifically, I started at the upper right back), picking up one stitch for every stitch along the back and one stitch for every row down the v-neck until you reach the center of the V.
Place a marker, then cast on one stitch onto the right needle using backward loop.
Pick up one stitch for every row up the other edge of the v-neck until you get back to where you started at the upper right back. Place a marker to indicate the beginning of your rounds from now on.
Now, when I did this I was using a 2x2 rib for the neck trim and I wanted there to be a 'K2' of the 2x2 rib on either side of the one stitch at the center of the V, so I counted out from the center of the V (not including the one center stitch) to see what stitch my round would need to start with in order for it to be symmetrical at the center. When I did it, it turned out that I would only have a 'K1' at the beginning of my round instead of a 'K2', so when I started the round I did a kfb in the first stitch and then continued on with P2, K2, etc.
So, just as an example if you were doing K2P2 rib like I was, this is what your rounds would look like:
Round 1: work K2, P2 ribbing to within 2 stitches of center marker; ssk, slip marker, K1, K2tog; work in K2, P2 rib to the end of the round
Round 2: work in established ribbing to within 2 stitches of center marker, ssk, slip marker, K1, K2tog, work in established ribbing to end of round.
Repeat round 2 for about 1" and then bind off loosely.
This is what my v-neck looks like.....I hope it's clear enough for you to see.