Perform passive ROM exercises to maitain the joint mobility and range. Do stretching exercises for the muscles which are tight. Encourge graded active ROM exercises for the muscles with grade 3 so that their power is increased gradually. Correct any deviation in gait and any balance problems. Knee Orthoses for knee control in sagittal plane are used to control genu recurvatum with minimal mediolateral stability. This type of Knee Orthosis includes a swedish Knee Cage and a three way Knee Stabilizer.
Apart from that do the stationary bicycling and walking on treadmill daily for building the endurance in the muscles. This will also improve his gait.