i went through the same thing when i was a sophomore in high school. i jumped up for a rebound, came down on someones foot, and ripped my ankle to shreds. i was un crutches, and i could not do anything without an air-cast for months. after the ankle healed it would give out on me in the same manner, and i had to always wear a brace.
i went to a few different trainers to ask what to do to solve the problem. heres the problem: ankle braces do not do anything to fix your ankle, they just provide stability (obviously). the problem occurs, because you become accostomed to having this extra support, and your ankle becomes dependant.
heres what he needs to do:
1.) go to a sporting goods store and purchase an elastic band (similar to a bunger cord). sit down and rest the leg on a chair, take the elastic band and use it to provide resistance while rotating your foot and pushing on the band, in a slow, controlled fashion.
2.) stand on only the injured leg, with the other leg bent at the knee. pretend he is on standing in the middle of a clock, keep your leg straight, and bend over to touch each number on the "clock", rising after each touch. count 2-3 seconds going down, and 2-3 seconds going up. it may not be easy, or even possible at first.
3.) do not run, squat, or do anything too strenuous until he has built up a decent level of stability and strength in the ankle. if he does not solve the problem now, he will be certain to have reinjuries down the line.