A scrim on a roll similar to those drop down screens for Presentations etc. might work.
Only sticking issue may well be the stifness of the scrim and its ability to roll neatly up and down into the housing without becoming creased etc.
Start off with beams, then have some "low" or extreme side ones whilst the scrim folds automagically down then WW the audience when images appear floating in the air.
With the right musical accompaniment that would be fandabidozy.
I'm getting shivers down the spine just thinking about it !!![]()