I understand you don't want the reflection up to merged layer when something written direcly to an underlying layer. Doubt its possible with bind alone (but that's just off the top of my head); with aufs maybe the =ro option for the relevant layer prevents further reflection after direct to layer writes? Not sure about that (still to test) or about when overlayfs used instead yet.
EDIT: For overlayfs such change apparently may or may not be reflected - according to kernel overlayfs documentation the result is 'undefined':
EDIT: no I think that for aufs the =ro layer option is only from the point of view of the merge result layer in that it tells aufs whether writes to merge layer can be written directly to relevant lower layer or whether a copy-up of file to writable upper layer is necessary (but again I haven't yet checked this). Basically I presently don't see how to achieve what you want... please let me know if you find solution!Changes to the underlying filesystems while part of a mounted overlay
filesystem are not allowed. If the underlying filesystem is changed,
the behavior of the overlay is undefined, though it will not result in
a crash or deadlock.
wiak