I find that I have similar questions to Gary. Will the relaxation help? Why is he being asked to do it? I'd like him to tell you what might happen if it doesn't work, and so on.
I'd really want to reach a shared understanding before jumping off into interventions. I think getting him to monitor and record his appraisals in problem situations would be really helpful in moving towards a formulation....which I don't think is there yet. The shared understanding may well lead to relaxation training, but I'd want him to tell me that.
I'd assume that his beliefs are well founded in evidence he finds convincing; for example, although he has never had an accident vis a vis his IBS, he may well believe that he has been lucky and only just missed having one.