Measure around the sole of the slipper and add one inch to the measurement. Cut two rectangles of fur. The length of the rectangles should be the same as the distance you calculated. The width of the rectangles should be the same as the desired height of the boots. Twelve inches is a good height.
Have the wearer put on the slippers while wearing his costume.
Wrap the fur around the sole of the slipper with the fur side in. Pin the ends of the fur together at the back of the slipper.
Starting at the toe of the slipper, pin the fabric together to form a boot shape. The line of pins will go along the top of the slipper and then turn and go up to the top of the boot making the classic boot shape. Have the wearer take off the fur boot so you can be sure the opening at the top is large enough.
Sew along the line of pins that forms the toe of the boot and the line of pins up the back of the boot. Remove the pins as you go.
Cut away the excess fabric, cutting 1/2 inch from the seam. Cut a slit in this seam allowance in the corner between the toe and the boot top.
Use this boot top as a pattern to make the other boot top. Sew it in the same way.
Turn the boot tops right side out. Run a line of hot glue around the outside edge of the sole on one of the slippers. Pull the boot top onto the slipper, placing the bottom edge over the glue. Glue the other boot top to the other slipper in the same way.