Tiptoeing back on-topic...
I can't hear anywhere on WISYA where Lindsey is pretending to be Stevie, so I agree that the Wikipedia entry writer is conflating different sources and drawing the wrong conclusion. But there are clearly other places where he has treated his voice to achieve a Stevie-like effect. Obviously the Big Love 'love grunts', but also the descending 'am what I am' middle section of Family Man, which sounds very Stevie-like at the start but reveals itself to be Lindsey as it heads down the register.
I've also never been really sure about that vocal collage part in the fade-out of Everywhere, which could be constructed from fragments sung by Stevie, but could equally be made from Lindsey or even Christine.