Measure just above your wrist where your thumb starts. Cut out two rectangles (one for each glove) with that width and the length you want the glove to be. Hem the top (and bottom if need be).

Pin the edges starting at the top. Mark thumb holes with safety pins. Continue pinning down the glove. One you are done just sew the seam until you hit the safety pin, stop, and restart sewing at the second safety pin.

Find some longish scraps (they don't have to be perfect). Pin one scrap to the glove at the glove seam just below the thumb hole. Sew this scrap on by sewing it down the seem. I had to hand sew this with the running stitch. Repeat for second glove. Put it on, tie scrap around wrist and you are done!