What about a boot parameter like live-media=only=udev=<udev match criteria>
I RFC for a boot parameter that I am about implementing:
live-media=only=udev=<udev match criteria>
where <udev match criteria> is the part of an udev/rule that do
selection of a /sys/ device.
It gives the user full control of which usb partition should hold live/
; more or less fine grained criteria can be used.
Threafter, /scripts/live will do an exclusive mount on the dev node
created by this rule, immediately after this dev node being created by
udev, either with a udevadm settle or a inotifywait.
Thanks for comments.