Well, I did it on my last one. I think I'll just continue the way I did the first few. I do a crochet-hook cast on - not provisional - leaving a long enough tail to sew the two edges together. After I cast off those 27 stitches, I abut the two edges and sort of weave them together. The resultant seam is flat to the touch but visible. It's not an elastic seam, so not suitable for anywhere elasticity is key. For the two or three inches of the hat's seam, elasticity is moot.
Thank you, it is most helpful