I agree with Marshall and a movement/gait evaluation might solve the problem. In addition to what was mentioned before, compression socks, extra salt, foam rolling, massages, better shoes, and maybe incorporating bare foot running might add to dexterity of his feet and aid in preventing cramps.
Over training might be something to look into as well. Too much milage and speed could be the cause as well.
Electrolyte solutions may not be enough sodium and potassium for him depending on the climate he trains in and the amount that he sweats. Personally, during my marathon training, because I train in sunny California, I need to not only supplement with electrolytes during runs but also over salt my food and add salt to my water throughout the day to prevent cramps.
I have great success with reducing cramping in clients with two things.
One, stretching the affected muscle frequently. This has been especially helpful with calf cramps.
Two, drinking a sport recovery drink.
For clients that experience cramping at night, they tell me keeping a sports drink on their night stand for this is helpful. And gentle stretching of the muscles affected right before bed or upon being woken by a cramp also helps. The gentle stretching also can be helpful in endurance events. The time lost to stretching beats crumpling in a heap from pain.
There are some other techniques that you can learn, but I would not be comfortable trying to explain them without including a hands on component with actual cramping athletes/clients.