I haven't done this myself, but if you set the Linode to use pv_grub (e.g., your own local kernel), and create a disk image large enough for your current root partition, you could then boot a recovery (Finnix) configuration, transfer over your old root partition to that disk image, and then boot from a configuration using it. Some configuration elements (interface names, IP addresses, etc..) might not port depending on your original hardware and network configuration, but that could be fixed via the LISH console if needed.
If you don't have any special requirements, you could then revert to a standard Linode kernel if you'd prefer.
I believe there's an article in the Linode Library -
http://library.linode.com/linode-platfo ... e-over-ssh - on doing a network transfer of disk images. This assumes you take down your source system to a maintenance mode too - e.g., boot a recovery CD of some sort on it. I think there's another library article on transferring a live system with rsync if the source system must remain running.
It's really easy to experiment with a Linode in terms of creating and destroying disk images and configurations, so if you haven't already I'd just give it a shot and see what happens. Your biggest issue is going to be the time to transfer the image, so if I were you I might create a smaller source configuration as a test to experiment with the process. You could even make it a VM with a minimal CentOS installation running on top of your existing system.
-- David