I was just thinking of something that will obviously never happen but the way Freddie could controll an audience I was wondering why he never attempted to get audience participation during the middle bit. That would've been a perfect audience participation vocal improv. Most of the vocal solo stuff seemed so force, the guitar one seemed to go perfectly with Now Im'm hjere, I think the vocal improv would have been a perfect fit for Bohemian Rhapsody. I'm sure that Freddie could've been up to the task in getting audience to participate I'm sure most knew the words. At the same time I bet that as something th band cosidered before deciding to play the tape.
I read that he was nervous the first time he did Somebody to Love live so maybe he was really nervous to do that part of Bohemian Rhapsody live. Its very complicated and maybe he didn't think it would sound right and would rather just play the tape than risk ruining the song.
It is quite complicated to do that part of Bohemian Rhapsody. If you are referring to the "I see a little silhuetto of a man..scaramouch...excuse me if I spelled that incorrectly" Yes, It is very difficult to perform it, as there are some words there like bismillah, which, maybe, some audience members might have trouble with. It also goes quite quickly and the audience might not catch up. I second 7 seas of rhye's response.