How to use the front camera with Tango?

Like lots of us, I guess, I discovered Tango today (one the greatest app !) As I own a Galaxy S, I wonder if we can use the front camera while talking. I know we can do that using the builtin visiocall app.

Does anybody know the hack ?

http://www.appbrain.com/app/tango-video-calls/com.sgiggle.production

Thanks.