Hey @msp welcome to the forums!
We don’t currently have an easy way to do this, but I’m interested to hear what your reasoning is - there might be a different way to achieve the same thing or perhaps a simple product change we can make if we can understand the full use case.
My immediate thought was that if you have or need images in your private docker hub registry, that you could use that as the primary source for distributing the images to your devices so that you’re not duplicating things. It is possible to create releases using images from a private Docker registry, see here: Develop locally - Balena Documentation
I’m not necessarily sure that it fits here, but I wonder if you have also looked at
buildx for creating multi-architecture images, I personally find this to be a pretty simple way of building images locally which can then be pushed to Docker. This is actually the process we currently use for a lot of our balena blocks - see here for an example: dashboard/build-images.sh at master · balenablocks/dashboard · GitHub
I hope this helps; by all means come back to us if not!