I decided to use fabric on the other pair of plaster casting soles. The orange silk I used for Jessica Rabbit's platform shoes gave nice results (although it was bit hard to handle), so I decided to use it.
I started by cutting pieces of the fabric and gluing the ends to the side of the sole. This seam will remain visible, so you need to make it as neat as possible. If you botch it, all is not lost as you can always glue some additional decorations on top of it. In fact, if your original plan is to use decorations, plan ahead and place the seam where it will be covered with them.
As the fabric is not glued to the sides of the soles anywhere else, it needs to be glued to both the top and bottom of the sole. I prefer to do the top first as it is the harder part. When that is done, all you need to do is to pull the fabric tight as you glue the bottom part.
Here you can see the insoles (leather and one layer of cardboard) and the leather pieces for the bottom of the soles. The uppers shown here are otherwise similar to those in Jessica's shoes, except they are made of cardboard. In this scale, it is easiest material to handle as it is sturdy, but not too thick. Bend the cardboard to the desired shape and keep it that way while gluing the fabric to get the best result. Finally, place the uppers on the correct position on top of the insoles and glue the ends of the fabric under the insoles in the usual way, cutting off any excess and making little triangular flaps.
I got so concentrated on making the rest that I forgot to take photos. Anyway, the part that will be behind the doll's heel is also cardboard covered the same way as the uppers. This time, I glued a piece of fabric also on the inside as it will show a little even when the shoes are on the doll's feet.
The straps are made of thin rubber band and go trough little loops glued to the inside of the shoes. This way, the straps are easy to replace later, if desired.
Here are the finished shoes on the doll's feet.
One thing you need to remember with this kind of shoes is that they cannot take any moisture. The plaster casting is basically unprotected as there is only a thin layer of silk on top of it. The same goes with the uppers made of cardboard. If you want a bit better protection for the plaster castings, use material that can be glued all over them. Then the glue and the thicker material will offer some protection against moisture.