Firmware Update from SD Card or RAM

I am working on a connector from iDigi (http://www.idigi.com) to the Arduino Mega. What I want to be able to do is to allow iDigi to update the firmware of my Arduino remotely. My plan for a first pass is the following:

  1. Use an Ethernet Shield with integrated SD card slot attached to the Arduino Mega

  2. Download the firmware from iDigi to the Arduino Mega’s SD slot

  3. Jump to a routine in RAM (or on the SD card) which contains just enough software to write the Atmel’s flash memory and write the new sketch

  4. Reboot!

I’m hoping to find somebody else who has already done this. Has anybody seen anything? The closest I can find is this approach which uses two Arduinos–the second tripping the bootloader of the unit to be updated: http://hackaday.com/2012/02/21/flash-an … n-sd-card/

I’ve also found some people who’ve started various bootloader projects but if at all possible I’d like to use the default bootloader.

Any ideas or references?