PyOxy could be a great complement to `shiv` (generates zipapps like you described). Shiv had system-installed python as a requirement, so this makes it fully portable.

https://shiv.readthedocs.io/en/latest/

EDIT: oh I just read through the PyOxidizer docs, seems like they already do have this capability as a goal, PyOxy is actually extracting out the shippable one-exec python out.