The recording part is the performance but in order to perform the parts they would first have to be composed. And I think we're getting stuck on the word "composed." I don't believe that anything was actually written down, but then I don't believe that Johnny Marr wrote out all of his guitar parts on notation paper. You can compose on tape. Listen to the interview if you haven't. Mike talks about the recording process and it's very interesting.
Mike could have recorded with the group or alone and it wouldn't really matter as to the time spent preparing. The thing is he did spend time composing his parts aside from the time he spent recording them.
No, I wasn't talking about composition because there is no point in getting bogged down with that.
You mentioned in your post (the emphasis is mine) that, "I don't think Johnny was hanging around watching Mike record his drum parts". That suggests that all 4 members would record entirely separately which is something that I have not heard suggested before.