Since they seem to be very stiff, making a sort of 'bootcover' with craft foam, or perhaps wonderflex might be the best way to go. I would start be making a duct tape pattern of the shoe, then adding on the parts that are sticking up with cardboard or something, this way you can mess around with how it looks until you're happy. Once you're happy with it, cut it off the shoe, and voila!, you have a pattern you can trace onto your final material.
A word of caution though, I did something similar on my Haseo Xth form shoes, and I attached them with hot glue. All seemed well until I got to the convention, where it was so hot the glue melted. Thankfully I was able to fix it with some super glue, and it held out for another two whole conventions with out any problems. The pieces on your shoes look like they have a whole lot more surface contact compared to what I had though, so I don't think this will be much of a problem for you.
Good luck, and I will be happy to answer any of your questions, if you have them!