Stretching may be an effective part of treatment for plantar fasciitis. There are some calf-stretching gadgets available, like the Prostretch Flexibility Exerciser. I’m sure they can stretch calves. However, stretch is stretch, and the calf is an easy muscle to stretch strongly — anyone can already apply as much of a stretch to the calf musculature as you can possibly tolerate. There’s not really any way to improve on that. My advice is not to bother: one less plastic doohickey in the world.