A few more cents.

The calves are the key to healing Achilles and Plantar tendon injuries. I'm a runner and have instances of both (Plantar is more of an issue for me). Working the Calves to loosen them up is the best thing you can do, but it requires more than just stretches.

I have a really hard foam roller that I roll my calves over at least once a day. Youtube is great for videos and examples. I shift myself with short directed rolls to specific spots on my calves and then shift my left position until I roll the whole calf out. i.e. rather than rolling over the whole calf at once, I might do it over 3 to 5 increments. I even roll the achilles out with pressure over the leg as it also helps stretch the achilles out.

The boot probably won't work for that tendon as it is more designed to stretch the plantar tendon out (and as a result compress the Achilles a bit... possibly).

I have to admit, I've never heard of the injury with respect to bicycling, so I wouldn't know a longer term solution. For running, the solution is about getting the angle between the heals and toes just right (balances between whether you'll tend towards achilles vs. plantar injuries). For biking, I could see the position of the foot on the pedals having a factor. Of course, I'm not sure that one can really control that as I don't ride with clips or anything related. Otherwise, it would seem a change in the bike-frame geometry (e.g. new bike) would be a factor.

Last, once everything is cleared up strength exercises and stretches for the legs are helpful for preventative work against recurrence. In all honesty, that has been the toughest thing to be disciplined in, and it has led to minor recurrences here and there over the years.