I had exactly the same problem a few weeks ago with one of my new clients. I didn't even know you could get such deep cracks in your feet, how naive? ANyway, I did a full CreativeSpa Pedicure and smoothed them as best I could with a callus smoother, put them in some heated booties lathered in massage oil, then retailed her some foot cream which she was to use every night, and booked her next pedicure for 2 weeks after. Her feet were a whole lot better last time I saw her, so they are on the mend, but I don't think there is a quick cure for extremely cracked heels. (Only what a chiropodist can do of course.)