How to add docker images to OS build?

Hello. I have a problem I’m trying to solve on my own for 2 days and it feels like I’m no closer to the answer.
I research ways to deploy rancher to ESXi without internet. Docker-machine works great and provides almost everything I need with one exception: as soon as machine starts to pull open-vm-tools image from internet. Until vm tools are running you can’t really do anything with the machine. And obviously if you don’t have internet on the server, you can’t use rancher.
I know that rancher supports custom registry for offline installation, but running different machine just for registry that would hold single image doesn’t sound optimal in any way. So instead I was thinking of creating custom rancheros.iso that would include latest vm tools image. I was thinking of adding image to /var/lib/rancher/preload/system-docker so it automatically loads on first start, but I just can’t find a way to add file to the image so it would appear in the installed system afterwards.
Can anyone please give me an advice on how to achieve this?