Set up a dynamic DNS with a subdomain?

Yes, via the API. Here's an example to get you started: https://github.com/snorp/linode/blob/ma … eDynDNS.py">https://github.com/snorp/linode/blob/master/LinodeDynDNS.py

Awesome! I actually had to use the script from this pull request though, as the API seems to have changed since the script was written: https://raw.github.com/Andomar/LinodeDy … eDynDNS.py">https://raw.github.com/Andomar/LinodeDynDns/90423fa02a99674145bb2aa759426d47ed6c0d7e/LinodeDynDNS.py

Obviously this requires you to run the script on your network somewhere, which can be a pain at times. Some routers offer Dynamic DNS features, which could be as simple as accessing a webpage somewhere. You could modify or take inspiration from that script to run on your linode. Of course, you would need to make sure it's adequately protected, and working as your router would expect.

I've set this up as a cron job on my NAS, which seems to work great.

I'm also using my Linode DNS for dynamic DNS. A cron job on my home file server checks the IP (by calling a script on the Linode) once a minute, and if it has changed, submits a Linode API request to update the IP (which has a small TTL).

Yes, I realize that you can simplify the script by just telling Linode (via the API) to update to your current IP address, but then you're hammering Linode's API servers once a minute (bad) instead of your own servers once a minute (acceptable).