OK but back to the original question-- despite any sh&t stirrers in the audience messing with Wikipedia, it is true that Lindsey has said on more than one occasion that he had to very much construct 'performances' from Stevie-- by literally cutting words or lines from all different takes and kluge-ing them together to sound like a single performance of the whole song. And that most of what sounds like her on background on his and Chris's songs was done with studio magic by him, altering his own voice digitally enough to make it sound like she is there in the mix.
I'm trying to figure out which are the most egregious examples of this-- whoever wrote the Wikipedia entry is wrong-- there are no vocals on Wassamatta baby that sound like Stevie that aren't actually Stevie- although you can tell in several sections where a vocal was taken from a different take and pasted in. And unlike one article said, LB doesn't sing the end of WISYA because she lost her voice but because he was trying to make a kinda drab song more interesting-- and having the male voice come in adds a totally different dynamic to the song (which totally works in my opinion).
She does sing the "can't disguise" on Little Lies, but probably nothing else. Anything sounding vaguely Stevie-ish is likely Lindsey's handiwork.
I never thought the grunts on Big Love sounded remotely like Stevie, but I guess I can see how very casual listeners might guess it was a woman and not Lindsey mucking with his own voice.
But I don't hear anything where I really think it's Stevie when it's not.