Wearing trainers with a rounded bottom (so it kind of rocks and stretches it out) helped me the first time. I also did some exercises like standing with the front of my feet on a step and dropping my heel down as another stretch.
I've got a worse spell this time though which won't go away (GP thinks I may have a heel spur though too). I've been doing some exercises in hydrotherapy, rolling a float dumbbell under my foot and doing calf stretches which help it a bit, limited effect but better than nothing :)