The fake-super emulation layer should be nestable, i.e., rsync with --fake-super should be able to correctly backup and restore a tree that itself contains fake-super information. For example, after the following commands, "file4" should have the same privileged attributes as "file":
rsync -aX -M--fake-super file file1
rsync -aX -M--fake-super file1 file2
rsync -aX --fake-super file2 file3
rsync -aX --fake-super file3 file4
One simple way to wrap a fake-super xattr for storing in another fake-super tree would be to add an extra "rsync." prefix.
Note that symlink munging, rsync's other feature that could be described as a emulation layer, is nestable.