Dear Blair, dear unknown stranger,
actually, that is exactly what we do using the custom items feature of ML.
In our experience, it is quite effective, i.e., participants usually believe they send an "email/instant message" to an audience. (We use the saying-is-believing paradigm in our research). We even implemented some kind of oneway chat in one of our experiments to make the interaction more "interactive" and believable, using Java Script.
In any case, what would really add some realism to this whole approach would be a full screen modus WITHOUT the black border. Blair, can you get rid of that?
Best
Rene