Good question; several interesting answers. With regard to the kinesiology of peroneal contraction keep in mind that the peroneals (peroneus longus & peroneus brevis) are interesting because they have plantar, lateral and dorsal pedal attachments. With regard to its pedal attachment, the peroneus longus muscle can be a secondary mover in dorsiflexion at the ankle (the anterior tibialis being a prime mover.) So, in addition to the exercises suggested which primarily overload ankle plantar flexion, have your client also perform dorsiflexion against resistance. I think that one of the best exercises for this is to resist the movement using theraband, or some other elastic resistance band. Wrap the band around the base of a immovable machine, couch or heavy chair. In a seated position facing the machine, or whatever, have your client plantar flex one ankle to full ROM plantar flexion. Wrap the band around the dorsal surface of the foot near the metatarsal-phalangeal joints. Have your client perform a warm-up set of full ROM dorsiflexion against the resistance band. Then, with at least a minute of rest between sets, use a resistance band that will challenge your client with 2-3 sets of dorsiflexion to 12-15 RM. Show your client how to focus the movement on the lateral side of the foot to fully engage the muscles of the tibial/fibular anterior compartment. Switch ankles and do the same on the other leg. I used this exercise regularly with the collegiate Nordic ski team I coached when the diagonal glide, not skating, was the typical stride.
Hope this helps. Take care.