Hi @zachgoll,
Unfortunately, right now, there’s no way to have preview-specific configuration for environment variables that isn’t defined directly in the render.yaml like the example you linked. One workaround I can think of is that you could have two env vars, one for prod and one for staging and then programmatically select between them in your application (I know this is not the most ideal situation). We have an open internal issue to track this type of request as it comes up quite often.