What you can do is every night before you sleep, put a layer of zam-buk or lotion on the cracks (clean feet). Then wrap it up with those kitchen clingwrap. Leave it until next day. Oh, don't expect miracle. With determination, you will get back uncrack sole.
My feet's condition was very bad despite seeing so many skin doctors. Luckily, I met a vey nice doctor who told me to wrap my feet to obtain moisture. They were completely healed after half of year of treatment and I did not suffer from cracked sole for many years.