Multilanguage audio in a single stream?

I'm streaming two languages simultaneously, one from a live camera and one from a live translator. Right now this is set up as two separate streams which works alright, but I'd like to combine the two audio streams so that a single recorded flv would contain all the audio with the client choosing the language of playback.

Is this doable with fms3? How have other people dealt with live-translated streams?

Any thoughts would be appreciated.