Yarok had some very good suggestions. I would recommend:

1. Mobilizations with movement:
-sustained lateral glide with pain free grip or with movement (apply & hold the glide, patient either grips or extends wrist, then release the glide)
-also consider performing a sustained PA glide of the radius on the ulna with pain free grip (if the above glide is not effective)
2. McConnell diamond box tape technique
3. Eccentric strengthening of both ECRB and supinator
4. General strengthening
-initial exercises: clench & open fist, against gravity wrist flexion & extension, gravity eliminated radial & ulnar deviation
-progress to: wrist flexion/extension/radial&ulnar deviation with 1 lb weight against gravity, pronation & supination of forearm with elbow flexed & supported, grip strength with theraputty or soft ball, twist towel into a roll, overhead triceps extension
5. Assess cervical & thoracic spine.
-often C2-T7 will have some form of segmental dysfunction.
-usually a lateral glide of the superior vertebrae (of the segment in question)
6. Check your neural tension by using an upper limb tension test biasing the radial nerve

Lisa