If the producers are pushing the show in Lee's direction then I don't blame them. They have millions of pounds riding on the show being a success and, frankly, Lee is the only one left who can deliver them that success.
The typical theatre-goer isn't a teenage girl - it's an older, wiser demographic who has seen many other stunning performances in their time and won't put up with something second-rate in the West End. The critics will not be kind to anything short of brilliant. They will be lining up to take pot-shots at the show. They would have loved to trash The Sound of Music, they don't like the idea of casting-by-TV, but Connie Fisher was so good they could only praise it. As someone who goes to the theatre two or three times a month, and has seen half of what's currently on at the West End, I can promise you that Lee is the only one who will keep the show still going this time next year.
In that respect, it wouldn't surprise me at all to learn that they rigged Josh's decision to let Lee sing. For a start he was the only one who had the right voice for it, and Josh wasn't there to give them support, guys, he was there to promote himself and sell a few albums!! So he would have agreed to do whatever. It would have sounded slightly embarassing for the others to have been singing with him, they just don't have the voices. But I think ALW has realised that the success of Joseph rests with Lee. Ben doesn't have the vocal ability, Lewis is a wet blanket, Keith is too annoying and childish, and Craig is too cheesy.
Rather than create a backlash for Lee over favouritism, I think it is far more likely that the performance of You Raise Me Up will have made a lot of people think "wow!" in a way that none of the others have done, and will generate more votes for Lee next week. Also, the edited VT showing the others being disappointed, may have been intended to show the others in a bad light (you never know how they're editing these things and what they choose to cut out) but Bill Kenwright's sarcasting barb at them afterwards - "my one abiding memory of this show will be the support you showed Lee, well done guys" - made it clear that the judges genuinely think there's some resentment going on behind the scenes.
Of course they'll be jealous of the attention that Lee's getting, but they are also proving to be ungracious and not very good actors - come on guys you could at least pretend to be happy for him - you're auditioning for an acting job, after all! Showbiz is about putting on a united front no matter how you're feeling. People who lose at the Oscars are obviously gutted but those who scowl get labelled as ungracious. Pop stars slating each other in public may be an attention-grabbing tactic, used because the genre is so utterly disposeable and has little to do with talent, but that kind of thing doesn't wash in other artistic circles where talent counts for more and what goes around comes around.
Sorry for the rant but I feel AWL is entirely justified in pushing Lee on the show as it is his investment on the line, and people who know theatre will know that Lee is the right choice. I have total faith in the GBP to follow his lead and choose the right Joseph. Before anyone starts bleating about this being opinion and not fact, of course it's all my opinion, but I honestly expect Lee to still be on the West End stage in 5 years time, and 10 years time, not in Joseph but in other leading roles, he will have a wonderful career after this. I don't feel the others have the necessary stage presence to hold a show.