To be honest, if I was sure, I wouldn't have posted the question.
The shop that had the "don't turbo a carbon frame" attitude showed me two bikes that were - apparently - messed up by a turbo. Both issues were in the same spot on the rear triangle, and resembled barely visible hair lines - these, I was told, were caused by a turbo and the rocking side to side rather than forward motion - more than that, I was told that they were fractures of the frame.
One owner came in at the time and confessed to using a turbo with the bike, and looked less than impressed at the news.
Other bike shop is much like you lot - says it's bullsh+t and I should enjoy the bike which I bought from him.
I'm thinking about roller bars to be on the safe side.