In Anatomy of a no-image workflow, I laid out an example no-image workflow using a .pkg with other .pkg files as payloads that get run with a postinstall script, and that's just because I forgot to turn off the rootVolumeOnly flag.
Well, if you actually remember to take that flag off, it's fairly simple to create a no-image using Packages. Here's how you do it....
For options, select Relocatable (this is allows you to install the resulting .pkg to another drive).
Import the packages you need. For the Munki tools packages, make sure you get the individual components, which you can get using AutoPkg.
You can install it by booting an external drive and installing the .pkg to the internal disk, or you can boot the never-booted Mac in target disk mode and then install the .pkg from another Mac.