Write code (for PIC or AMTEL) to allow multiple sources (camera and controller) to read write to the same SD card

Programmer required to write library to allow multiple sources (camera and the micro processor) to read and write to the same SD card. The micro to mimic a SD to the camera. I expect camera to have SD extension to the micro and then micro to imitate/mimic an SD card and copy the read bytes into the real SD card. Then the main application will also read/write from this real SD card. The Micro selected is on the Freelancers advise, prefer something can can be purchased in a development board - like chipKit or similar. I will develop the main application, just need a library created that can allow the SD functionality.