ALSA/mplayer dynamic audio channel mapping?

[fatfatwolf]

I was wondering if there's any plugin (or something similar) for ALSA or mplayer, so that I could change the audio channel mapping on-the-fly. For example, I can start playing an mp3 file with both speaker output the left channel, and after 1 min switch both of them to the right channel without stopping the application and start over. That'll be useful. Any suggestions are welcome, and thanks in advance.