I am currently dealing with this condition and am doing two things that have helped me get better:
The Strausberg Sock. I stumbled on this product while reading about this problem other people were having in another post, Though I can't remember if it was on this forum or the Road Forum. It is a full coverage sock that has a strap and will hold your foot at a 90 degree angle for however long you care to use it. I use it over night. A google search will get you plenty more information on it. I got mine and a local store that specifically catered to Runners and Marathon/Triathlon people. One suggestion I have is to wash the thing a couple of times before you use it. I did not do that and my legs broke out in a rash that required me to use lotions like I had Poison Ivy before it cleared up and I could continue to use the sock.
Change out the insoles in my shoes for more arch and heel support. This has helped a lot though it took a lot of getting used to. I use Super Feet in my cycling shoes and am experimenting with Dr Scholes Athletic insoles for my everyday work shoes. I have tried some other brands but so far these have been the best I have found for me. YMMV. Good luck and let us know how it works out.