Attendance at Appeal

My son is 18, he was on DLA (MRC LRM) since he was 10, went for PIP. He was v.anxious at the f2f I had to go with him or he wouldn't have gone. The assessor was unsympathetic to his anxiety/ASD, I had to answer most of the questions. We also had an advocate with us. He was turned down 0 points, mainly due to the info on the assessors report which said he did not have any problems answering questions, showed no signs of anxiety, and because he has GCSE maths he is fine. He also has a history of self harm. I got extra evidence from an ASD charity we are involved in and asked for MR, pointed out again the difficulties he has socially etc. but again he got 0 points and the decision maker reffered to the assessors report and ignored the ASD report. I am keen to go to tribunal (and put in a complaint about the assessor, the advocate has written a letter to give her opinion of the f2f), but my son was traumatised by it all and he refuses to go to a hearing. I am his appointee.
Can I arrange an appeal and on the day just I attend and say he will not attend (which is true)?
Has anyone done this? Or any ideas for an alternative?
Thank You