No, it wouldn't be too hard.
Here's a live demo where we turn a small crowd & their devices into the movie's sound system. http://vimeo.com/71647538
Here's a live demo where we turn a small crowd & their devices into the movie's sound system. http://vimeo.com/71647538
Here's the movie clip I speak of above http://vimeo.com/m/93899424
This is new(ish) type of technology that requires solid and FAST Internet. It may or may not work in various countries based on Internet speeds (10Mbps or higher is recommended ... Possibly 5Mbps of higher could work too. )
Or better yet, if the audience is on numbered seats, print a QR code on their ticket which gives them an URL that includes their seat number as a parameter.