I'm thinking something more like Tree of Life at Animal Kingdom. Random shows occurring every 5-10 mins, keeping crowds flowing.
Tree of Life and Discovery Island has a great deal of crowd flow space to allow these shows to happen.
Where? Shrek's roof? There isn't exactly a lot of available space for them to just plop a set bleachers down. They literally built the media bleachers on top of parts of the land for the grand opening.
There's room in FJ's extended queue if needed, and by the FJ exit as well. I'm just spitballing ideas because otherwise I have no clue how they'll pull this off at USH. Maybe they'll indeed just have to stop traffic or maybe even just stock people inside the FJ extended queue. (not the greenhouse obviously)