This can be done with a FUSE server. By using filesystem namespaces, an app can then be restricted to just the view of the filesystem that this FUSE server expo

This can be done with a FUSE server. By using filesystem namespaces, an app can then be restricted to just the view of the filesystem that this FUSE server exposes. Another possibility, at least for dynamically linked programs, would be to set LD_LIBRARY_PATH to force every system call through a wrapper.