Which (if any) union filesystems allow you to mount them without an underlying filesystem?

I am considering using a union filesystem, such as aufs, UnionFS or OverlayFS. I have a 138GB of Android source, to which I want to make minor changes and keep them under version control. My plan is to mount a unionfs on top of the (now read-only) Android source, and make edits on the unionfs. In order to commit changes to version control, I will also need to have a view of the unionfs *without* the underlying, read-only, Android source. Do any of the union filesystems allow a volume to be mounted simultaneously with and without an underlying filesystem? (If not the strategy could still work, but would require some unmounting and mounting around every commit.)