How can I transfer my Hard Drive storage into a new Xbox 360?

Hi, I have a refurbished 360 Pro that just recently got the RROD. I AM planning on sending it to microsoft, and I AM planning on trading it in to Gamestop for a 360 Elite as soon as I get it back(so they can't refuse it due to RROD). What I would like to know is that is there any way for me to transfer my Hard Drive memory between consoles? I know about the Data Transfer Cable, but my concern is how I will be able to transfer data to my new console as I would have LITERALLY just traded in my old one. There is the possibility of buying a third backup Hard Drive as an in between mule, but I don't want to spend the extra money. Also, there is the possibility of buying the Elite first, transferring the data, and THEN trading in my Pro; but that requires me to fork over a lot of money up front when all I may end up with is store credit. Any ideas? Please no answers from people telling me to buy a PS3, I know a lot about the pros and cons of each system and am a very proud and satisfied owner of a 360.