Custom CA Cert on Rancher Nodes

I need to install a custom root CA on AWS nodes created by Rancher so that they can pull images from a private registry. I tried adding the root CA as per this but this did not work.

My other options to this are as follows, along with some questions I have for each approach:

  1. Create AMI with CA: This would require me to re-build AMIs for every new version of RancherOS.
  2. Use cloud-config: I see this as the ideal option. However, I do not see a way to use this in the Rancher UI.

Is there a better way to achieve what I want?