A friend of mine (who is very experienced in this subject) recently did this DIY foot shortening — and this definitely has to be the limits of what’s possible in a DIY setting. I hope it heals well (it’s two weeks old in this photo)! More pictures are in BME/extreme‘s amputation galleries.
PS. It’s quite an old interview, but you may want to read this interview about voluntary amputation (free link) if you’d like to learn a little more about the “why” end of things, or if you’re a BME/Video member, this video interview about ampuation (as well as a demonstration) is very much worth checking out.