Dr vincent Carbone has a great "Reducing Problem Behaviors in Students with Autism" Program. Some time its as easy as saying stop scripting while we work ,then tell them they will get a scripting break. Worked for us.
Personally, I had this same problem, and I had to take away everything that he got his scripts from. No more TV, no more V-Tech toys, no more movies, etc. It's hard but it works. We now live in an almost completely electronic-free home (I have a secret laptop I use at night!).
I have a student that does this throughout the day. When he does this I give a physical prompt (touch his chin) and say "Focus". He repeats this which interrupts the scripting. I also write ________ needs to focus and he reads this and this helps reduce it somewhat.
He repeats what he has heard on the tv, computer, books on tape. Example, He is in speech therapy, and they are telling him to do something, he is resiting the Skippy Jon-jones book, or the Mickey Mouse Club House song. He does this alot. He used to be able to script, and still respond to questions, etc. Now he appears to be to deep in the script, and frequently not responding.