Trading 360 elite for 360 slim...?

so pretty much GAME have an offer where you can trade your elite in and get the new one for just 100. i am running out of memory, cant really play kinect online as my wireless adaptor takes up the port and iv had it a while so its due to break soon. if i were to do this how would i be able to keep game saves? i know i can just recover the profile so thats ok but iv almost completed LA noire 100% and want to keep that save, i can just redownload DLC. i know putting it on USB wouldnt work as the new xbox would reformat it deleting everything on it anyway and the shop probably wont let me take the harddrive home. any suggestions????