It is possible to back up the information, however I have never had to move the information back before.. I will post the instructions for backing up the data and you're going to need to try some things to get it from the External back to the drive, but it shouldn't be too hard.
#~ mkdir /media/disk
#~ mount /dev/sdc1 /media/disk/
#~ dd if=/dev/sda/ | bzip -z > /media/disk/backup.bz2
(#~ is a new line of script, sdc1 is the external drive in my case, and sda is my entire internal harddrive) (So you'll need to replace those with your own values, I hope you're successful)
p.s. Also if you're able to send the compressed backup back to your computer successfully.. Could you let me know how you did it?