Peel cup back as it melts. Do this for 15 minutes each time. This works great for other injuries, but is excellent for this one. Check your shoes and your running style. In racewalkers this is most common when either increasing mileage too quickly OR if the heel of the shoe is too high.
Race walking strengthens the front of the leg like nothing else except x-c skiing and speed skating.
Hope this helps. Joel, the only thing you are compromising is possibly some arch support and cushioning. Since you need less cushioning than Nike tends to provide for trail running, I don't see that as a problem. I didn't know you could have both flat and rigid feet at the same time. Rigid tends to go with high arch, instep.