You can do it on the console in the digital patching menu as of firmware version 1.7.
1. On the console, press Home.
2. Select Audio Routing on the screen.
3. Select Digital Patching.
4. On the screen, select which input channel on the console you want playback on.
5. Select the USB icon under the Assigned Source column.
6. Select the USB source you want to playback from.