Apart from stimulation there are alternative muscle re-education techniques ,kinesio taping can be done to facilitate the muscle. Hope he is wearing a dynamic cock - up splint,if not buy that immediately and start wearing it. Give him exercises in gravity elimination(tell this to your physiotherapist).
Next Steps
give him food rich in vit B 12( sprouted green grams, groundnut, spinach,papaya,almonds etc)
Health Tips
cut down on coffee,white
sugar ,tea,junk food,etc. all the above can be tried to the maximum extent before surgery