The Florida based company Tire Alert (www.tirealert.com) fixes sewups. He has a special machine and removed the entire inner tube and replaces it with a new one. He fixed a Conti Altanta Gold for me and did a great job. It is also worth trying the Tufo leak sealant if the puncture is small. I'm still riding a sewup that I fixed with the sealant three years ago.
Del Mar CA