I always thought that, given the range of the melodies DT writes for James, a female singer could easily have fit the spot very well. In fact, of the vocal covers I've seen of early DT material, the women were usually the only ones who could do it justice.
Two questions:
a) Did they consider a female singer in the early days when they were shopping for singers? (Is that mentioned in Lifting Shadows, or an interview?)
b) Who do you think could have done a good job?