Transferring files to an arduino SD card shield over serial or usb?

There's a library that lets the arduino playback audio files read from the SD card. I want to try to eliminate the need to take out the sd card and just plug in the usb of the arduino and send 1 file to it over the serial data. This would take a dedicated program on your PC to covert the audio files into serial data that will send it to the arduino and the arduino itself to re-assemble the data into the file, overwriting the existing file on the sd card.

Any ideas?

The Teensy guys are working on this. Have a look on the PJRC.com forums. I think this problem has been partially solved for the Teensy 3.5 and 3.6.

MorganS:
The Teensy guys are working on this. Have a look on the PJRC.com forums. I think this problem has been partially solved for the Teensy 3.5 and 3.6.

Yeah their teensy audio project was one that caught my attention first. Only issue is that there are modules/shields that use an outboard decoder to access the sd card and playback the audio and then there are solutions that use the actual atmega chip to process the audio and use a parallel Digital to Analog converter for the actual playback. Since I'm tryng to figure out how to send files over serial (and I really only need to send one file and only one file will exist in the flash at a time) the teensy solution would not be the one I need.

Just to clarify, it's not the audio playback part but the file transfer over serial part