Severe blocker being fluent in drills

DANIEL, 20, California, very severe stutter-on-every-word in all conversations. Urged him to hum into all words and link to a stop in our first Skype a week ago. No progress because he hesitates after every hum and then blocks the words. In drills today, he hummed-linked-stopped no problem. Told him that he MUST do this 24/7, or he'll continue to block most words.