Rebuild your Linode using Debian 7.5 x64 and set the size to 1GB (we need this partition for GRUB) Set the root password to anything, as you won't ever boot Debian again.

Create a raw disk, spanning the rest of the Linode called 'CoreOS'; add this to the profile in between the swap and Debian disk.

Boot your Linode and SSH into it as root.

wget the CoreOS installer to a directory on your debian install. Create a cloud-config.yaml with your private key (directions here)

Run ./coreos-install -d /dev/xvdb -c cloud-config.yaml

After the script succeeds, run the following:

mkdir /mnt/core-boot
rm -rf /boot/grub
mv /mnt/core-boot/boot/grub /boot
Now run vi /boot/grub/menu.lst. Change all instances of root (hd0,0) to root (hd1,0) On the next boot, you can log into Core by running ssh core@<yourserver-ip>. The SSH key you added before will allow you to log in.