[U-Boot] Composing multiple envs

I'm trying to set up a configuration where I've largely got a hardcoded environment (ENV_IS_NOWHERE) with a very small list of variables that come from a loadable environment (ENV_IS_IN_FAT for my use case) - things like serial# and regulatory region. Even then I want them largely set once in the factory and not really written again.

I could've sworn I'd seen patches that implemented this kind of thing around the time of the environment rework, but I'm failing to find them either merged or pending.

Am I imagining it and should just go and code it up? Feels like most of the pieces I'd need are there.

-- Alex Kiernan