I've been reading around and it is not clear to me whether Apple will be happy if I do this. In fact, I get the impression that they won't (I'll get rejected). Even camera apps are on thin ice. I think this is only acceptable in camera apps where it's used judiciously.
I'll phone Apple dev support and ask but I'm not expecting to get an answer. In the past, the people on the other side of the phone seemed to be uncomfortable committing and giving a straight yes/no answer.