Yes, you can do the neck on either a circ or dpn's, and you won't have to rip out any seams.
Start at the back right seam, pick up and knit the 30 stitches of the back neck holder, procede around the neck either picking up the stitches from the holders or the 12 stitches from the left and right neck edges. When you're done you'll have eighty two stitches on the circ ( or dpns) then work the neck in the round. Your join will be at the back right shoulder.
You may need to change the neck instructions to work it in the round - for example (I haven't looked at this particular pattern) if the neck is finished in stockinette stitch, the back and forth directions would have you purling one row, then knitting, then purling, etc. for however many rows you need. To do it in the round you'd just knit every stitch, every round until the neck is long enough. If the neck is folded over and seamed down make sure you double check which side of your round will be the right side.
If you have any other questions just write back.
Aren't you glad you don't have to
Happy Knitting :XX: :XX: