If there is a piece of net or lace between the seams, you should still be able to sew the hair to it. (Some wigs don't have a net, just horizontal elastic wefts, but they have the vertical stripes to keep them in place instead).
You should still be able to pull sections of hair through the netting; you'll just need to be careful and do it in a straight line down the center back. Perhaps baste a ribbon down the center or something?
The International Costuming Convention is returning to Toronto Canada!
4 Days! 4 Masquerades! Shopping, Tours, Parties, Costuming Panels and Classes, Cosplay, Props, Doll Show & Competitions, Steampunk, Sci-fi, Fantasy, and so much more!