I made use of leftover materials seen here and here, and I get to take this baby for a spin this very day! Follow the instructions after the jump and be prepared to dazzle border patrol.
1. Scrap leather
3. Needle and thread
4. Glue or sewing machine
1. The materials.
2. Trim the leather so that it just fits over your passport when folded in half.
3. Cut a piece of ribbon about 12 inches (which works for my U.S. passport and, I imagine, should work for others. You want the ribbon to be 2x the vertical edge of the passport plus about 2 inches). On the right side of the leather, center the ribbon along one vertical edge. Make sure it sticks out over the edge a tiny bit, about 1/8". Clip in place.
4. Flip it over and attach the ribbon with glue, or sew it down along the side farther from the edge of the leather.
5. Flip it over again and fold ends of the ribbon in towards each other. Make sure that the ends of the ribbon are pulled in as tightly as possible without bending the leather. Fold the top end of the ribbon under and hand-stitch it into place securely. Sew together the sides of the ribbon along the edge of the leather. Repeat steps 3-5 on the other side.
6. Tuck the covers of your passport behind each ribbon flap. ¡Buen viaje!