Another half-useful result of my experiments:

Looking at the code of the recaller widget, one sees that it is possible to use the output of a pulse sink (at least the internals) as a gstreamer source and therefore play it back via usb:

This plays back the output of the internal music player (perhaps any sound application that uses pulseAudio) through usb. There are two pitfalls:

• The normal output is not muted (minor problem I would guess and maybe solvable with alsamixer - as it should work on a lower level than pulse audio
• The audio stutters a lot (at least for me) - making this unusable for anything serious

Could someone try the above command on his/her setup? My device is not overclocked, and maybe it depends also on the external hardware. Be warned though, I got occasional reboots.

//EDIT:

To try this, just type the above in an xterm and play something back through the stock media player.