[Fedora-livecd-list] mounting a persistent overlay

Can anyone tell me how to mount the squashfs / persistent overlay on a live USB stick, without booting it up? Context: I gave someone a live USB stick with something in /etc/rc.d/rc.local to log some diagnostics when he booted it up on a machine in China. Now I want to get the logs off the USB stick, but I am just realising in my amateurish way that when I boot it up I will overwrite the logs... Such is the problem with operating under time pressure... James